Odorless Cat Litter Box

Cat litter boxes stink to high heaven. Worse, many cat owners gradually acclimate to the odor, creating an awkward situation for house guests. If you are a cat owner, this DIY catbox ventilation system will dramatically improve the quality of your life, restore your fraying friendships, and amuse guests with your ingenuity. Your cats will probably even forgive you for not scooping as often.

This design is intended for those who are willing to keep the litter box near a single-hung window with outer screening and no burglary concerns (i.e. probably not on the ground floor in a neighborhood like mine!). I will be following up this post with another version that couples to a bathroom exhaust vent.

This project is designed to cost less than $35 to make, and uses mostly common, recycled and/or re-purposed and cheap materials. It is also quite doable for someone with limited tools. Perfect for apartment dwellers!

Required Tools
* Hot glue gun and roughly 10 hot glue sticks
* Heavy duty poultry shears or tin snips
* Serrated bread knife
* Serrated tomato knife
* Electric drill
* Standard drill bit index (up to 1/2")
* Permanent marker

Required Materials
* Hooded plastic cat litter box with at least 7"x7" of flat surface on the back end
* 12V 120mm CPU fan (smaller sizes may also work...try recycling one from an old desktop computer). I used this one.
* 12V DC power adapter (500ma). I used this one.
* 2 x plastic food storage containers (25oz, 740ml - 6-3/4" x 6-3/4" x 2-1/4") with lids
* 2 x empty, de-labeled 28oz food cans (I used cans from crushed tomatoes) with both ends removed.
* approx. 10 hot glue sticks
* 5-25' (location dependent) of 4" dryer duct, aluminum or plastic
* electrical tape
* 2 x 16" long zip ties
* 2 small zip ties
* 8" x 36" rectangle of Owens-Corning Foamular(R) 250 or comparable (pink foundation insulation) or 3/4" plywood (if you have a jigsaw or sawzall).

Step 1: Replace Catbox Air Filters With Cardboard

Most hooded litter boxes have these silly "air filters" that slide into openings on the top-back of the hood and look like grey pot-scrubbing pads.  They do nothing to remove any of the smells...pure gimmick.  With our new fan-exhaust system, we will want air to draw in from the front opening of the hood, across the litter, and out the back.  Because the vents that come with the catbox are positioned at the top back of the cat-box, we will want to cover them to improve airflow from front to back.  Trace their exact shape on some corrugated cardboard twice, so you can have a double thickness to match the thickness of the filter slot.  Insert and trim.  

Step 2: Build duct flanges from empty food cans and leftover containers!

Large empty food cans (28oz) are close enough in diameter to be re-purposed into a great adapter for standard 4" flexible dryer duct hose.  Tin snips or well-made, heavy-duty poultry shears easily cut through the can.  Combine with a standard square disposable 25oz plastic leftover / freezer container and some generous beads of hot glue to seal the deal, and for around $1 you have effectively built a dryer duct flange.  Keep the container lid handy as we will use it later as an an air-tight coupling mount on the back of the catbox.

Step 3: Mount the Fan and Attach the Power Adapter

Get to know your fan and understand it's directionality and the polarity of your 12V adapter so you can be sure your are facing the fan the correct direction when you glue it into the leftover container part of your home-made dryer duct adapter. Strip the ends of the leads and conntect them to your power adapter.  If the fan doesn't run at first, reverse the leads on the adapter, as polarity seems to matter on these fans. Face the fan so that it will blow OUT of the the can side of the duct flange. Cut a small slit in the side of the container closest to the wire leads for the fan and pass them through.  Use four generous blobs of hot glue and press and hold the fan firmly in place until the glue hardens.  Use another blob of hot glue to seal and secure the wire leads passing through the container.  Strip the leads of both the power adapter and the fan.  Twist connections and wrap with electrical tape.  Tie a knot in the wire above the wire splice to provide stress protection in the cord.

Step 4: Seal Container Lid to Back of Catbox Hood

The lid to the leftover container is going to serve as a kind of airtight coupling that will hold and seal the hose adapter / fan unit on the back of the cat litter box.  Use a permanent marker to outline the container lid in the center of the flat plastic back of the litter box hood.  Get your glue gun good and hot and have several extra glue sticks on hand.  Run a generous bead of hot glue just inside the permanent marker line so that it will create an airtight seal with the lid.  Press the lid firmly on the hot glue until it sets.  Press the center of the lid to listen for air leaks from the air trapped between the food container lid and the plastic litter box.  Most likely you will need to run several more beads of hot glue around the edge of the container lid to seal it to the litter box.

Step 5: Drill Vent Holes in Litter Box Hood

Once you are satisfied with the seal between the container lid and the back of the catbox, use your shears to cut away a square-ish, roughly 5"x5" center from the lid. Put another bead of hot glue around the inside of the container-lid / catbox-hood joint. Grab your drill and a large (1/2" is what I used) drillbit. Improvise a regular pattern of holes covering the area inside the cut out area, leaving only enough of a plastic to create a barrier that will prevent your cat's tail or fur from being drawn into the whirring fan blades, but that allows for a maximum of air flow. Use your shears to clean up the holes. Check that your homemade fan housing / hose adapter fits snugly onto the litter box. You may eventually choose to glue the assembly together. I chose to leave mine removable so the hood can be easily cleaned with water without damaging the fan.

Step 6: Measure and Cut Foam Rectangle for Window

Because most apartment dwellers don't have ready access to electric saws, I opted to use 1" thick Owens-Corning pink foundation insulation: it can be easily cut with a serrated bread knife.  I bought a whole sheet of it for pretty cheap at a Home Depot in the Bronx and cut it down some using a handsaw in the store to allow me to get it on public transit.   The pink insulation could probably be painted with acrylic wall paint to improve appearance.  Another bonus is that it provides insulation comparable or better than window glass.

Use a tape measure to to get the inside dimensions of the track that your lower double-hung window slides in.  Use a straight edge to mark a rectangle 8" by the width of your window frame.   Use a large, serrated knife to cut the rectangle from the stock.  Be sure to support the material as you cut, as it cracks somewhat easily.

Test the fit of the foam in the window and trim accordingly.  I had to compress the foam some with the palm of my hand to get it to fit in the window track, but it's going to make a really tight seal against the cold NYC winters as a result!   I also found that the seal with the window was improved by using the tongue side of the tongue-and groove as the top edge of the window insert.

Step 7: Build the Exhaust Vent Fixture

You're essentially going to be making a home-made version of a through-wall dryer exhaust vent. If money is no object and you don't want the fuss, there are kits available for this in most corner hardware stores. Homeowners may also prefer a less homespun approach or a through-wall option, which is afforded by the long duct collar on most commercially available duct vent kits.

Nevertheless, you want the affordability, challenge and fun of re-making this with tin cans and tupperware, read on! It's important that our design keep out the rain and wind, so we're going to use a 2nd leftover container and lid to build a rain/weather hood, with a backdraft-preventer flap made from the extra center stock we cut earlier while making the fan housing. To connect the flap with small zip-ties, drill two small holes per side in the lid and one larger hole per side in the flap and pass the zip-ties through as shown in the photos. The zip ties should pass easily through the flap, allowing it to hang and swing freely.

Note that the container bottom is going to serve as a rain hood on the outside of the window divider. Cut a rectangular portion out of one side of the container, which will face downwards, allowing air to escape. (See last several photos for detail)

Step 8: Cut Through Window Insert and Mount the Vent

Position the litter box in your space and determine the best location for the dryer duct to pass through the window insert. Trace the outline of the can on the insert to suit your chosen location.  Remove the insert from the window and use a large (1/2" or so) drill bit to perforate the inner perimeter of the circle.  Use a serrated knife to gently cut a clean circle from the foam.  Insert the vent through the foam to test the fit.  Clean the hole as needed.  Trace the outline of the container lid on the foam in its fully-inserted position.  Run a thick bead of hot glue around the inner perimeter of the traced line. Press and hold the lid against the foam until the glue sets.  Now glue the bottom of the food container into the lid.  From the inside of the window insert, inject blobs of glue around the body of the can to help hold it in place.  Install the window-insert and cinch down the duct using a large zip tie.  

Plug in, kick back, and enjoy an odorless litter box!  I enjoyed creating some smoke with burning paper just to observe the draft of air passing through the mouth of the litter box hood and out the window.  

Step 9: Arduino Extension and a Bathroom Vent Version

Some cats can be extremely finicky about changes or slight noise in the cat-box, and may start crapping all over the place as a result.  If this ends up being the case, you might consider tweaking this design to put the fan on the window-end of the system.   If you want a further challenge, try rigging up two PIR sensors with an Arduino and a relay switch for the fan like I did for my Mom.  The fan shuts off whenever the cat comes near the litter box, and stays off for 30 seconds after the last detected motion.  Problem solved! Lot's of fun.

If you prefer to have the litter box in a bathroom, you can build a homemade hose coupling that fits over the bathroom exhaust fan / vent.  Because 4" duct is a bit unsightly snaking up to the ceiling, it's probably worth using a design with smaller diameter hose, like 2.5" sump pump hose.  Smaller cans, like those used for tomato paste, could provide the way here...

Comments

[midvale530]

Astilly,

Thanks very much for the great design. I followed it closely and am very pleased with the outcome. The project also introduced me to hot glue, which is fantastic. Our litter box is in the basement and the odor was coming up the stairs into our living space, in addition to the unpleasantness of going into the basement. I had to modify the window attachment scheme because of my particular circumstances but I stuck to your general principles. My only comment is that, due to the airflow in our house we might need more fan power to overcome the expected draft when we run our wood stove upstairs in the winter. If necessary I will install a second fan at the window side. What do you think? Again, many thanks for posting. I'm so much happier with the fresh air!

[IAmHeisenberg]

Would you mind making a DIY for your Arduino system? I'm not very familiar with them and would love to learn how to make PIR system for my litter box. Great DIY by the way.

[shellyrae]

Excellent instructable. Just an opinion on the filter that fits into the top of the cat box: I actually find that it works VERY well. I can definitely smell when it's time to change the filter - when I do I have to put it in a ziplock and secure it well because it REEKS. New filter = no stink.

[EJGilson]

A helpful tip for those who do like the filters on the top of the litter box: a dryer softener sheet and a piece of tape work wonders to absorb litter box odors, and are much cheaper than the filters they sell at the store. :)

[RustyRoller]

LOVE this -- thanks!

Tiny idea / improvement: When drilling the holes in the back of litter box, take lid off and drill from inside the lid. That way, most rough edges will be outside the box and you won't have to worry as much about tail or body getting injured by jagged edges. Also, could probably just use a power sander to lightly smooth over holes all at once.

For really long-haired kitties, glue a piece of window screen over the area where holes are! Or, if you've got really curious cats, do this to keep their noses and whiskers from intruding through holes, along with any stray bits of litter that get kicked up.

[jimbo13]

you can run it with a 3 watt solar panel all day for free.

[astilly]

Very cool suggestion. I could imagine the solar panel being mounted outside on the window divider or on the outside of the rain hood. Seems like you'd need a rechargeable battery to keep things moving at night, which starts to become complicated, expensive, and higher impact...do you know of a simple solution here?

[Simpson21]

you can find some easy setup stuff try adafruit and sparkfun they both have a good amount of solar parts.

Thanks for posting the code below. I have started writing up code for both 2 and 4 wire fans. (2 or 3 wire fans take V+ Ground, 3 wire also out puts speed of fan. 4 wire fans also have PWM input for speed.)

One of my cats has a problem with trying to attack the fan when its spinning at high speeds so I had to come up with a way to have it spin at around 30% of top speed. the newest fan in question is off of a nvida 8800 video card thats long been dead. The 4 wire fan from it has really saved me on speed control but I still made it for both types of fans just in case.

Along with the solar idea My code would most likely be easy on the power consumption as its not running all the time but starts slow when the cat enters the box waits till it leaves then turns it on full to make sure no air born smells get back in to the room.

I will try to get pics of the box and fan setup soon to show how I made it. Who knows you might even change yours to run like this if the cats dont mind.

[stevezone]

My friend and I thought of this and tried it over 10 years ago... the results were astounding...
The cat entered the catbox and proceeded to commence it's business, the fan turned on, literally scaring the poop out of the cat and caused the cat to go ballistic! The cover was thrown off the catbox, cat litter and poop spread all over and the cat departed at high speed for the closest convenient hiding place.
We nearly died laughing!
So this ought to be good for a laugh anyway... but beware, you may permanently traumatize your cat!

[astilly]

I've found now, with three of these in operation in different households, that an "always on" quiet CPU fan doesn't seem to bother most cats. My mom's cat was the only exception, but then again I used a 120V model that was slightly louder than the rest, so it was hard to tell. See the Arduino extension for the sensitive cat owner's version.

[Simpson21]

Really good idea. I have started working on this for my cats. Do you mind posting your arduino code. I would really like to look at it and improve on mine.

[astilly]

The Arduino add-on is truly optional. I wouldn't bother unless your cats prove unable to handle the noise. Here's the code nonetheless. Note that I used an inverter chip to take every "HIGH" to "LOW" and vice versa. This is probably possible by altering the code to give the inverse behavior, though I wasn't successful in figuring this out.

/*
* //////////////////////////////////////////////////
* //making sense of the Parallax PIR sensor's output
* //////////////////////////////////////////////////
*
* Switches a LED according to the state of the sensors output pin.
* Determines the beginning and end of continuous motion sequences.
*
* @author: Kristian Gohlke / krigoo (_) gmail (_) com / http://krx.at
* @date: 3. September 2006
*
* kr1 (cleft) 2006
* released under a creative commons "Attribution-NonCommercial-ShareAlike 2.0" license
* http://creativecommons.org/licenses/by-nc-sa/2.0/de/
*
*
* The Parallax PIR Sensor is an easy to use digital infrared motion sensor module.
* (http://www.parallax.com/detail.asp?product_id=555-28027)
*
* The sensor's output pin goes to HIGH if motion is present.
* However, even if motion is present it goes to LOW from time to time,
* which might give the impression no motion is present.
* This program deals with this issue by ignoring LOW-phases shorter than a given time,
* assuming continuous motion is present during these phases.
*
*/

/////////////////////////////
//VARS
//the time we give the sensor to calibrate (10-60 secs according to the datasheet)
int calibrationTime = 10;

//the time when the sensor outputs a low impulse
long unsigned int lowIn;

//the amount of milliseconds the sensor has to be low
//before we assume all motion has stopped
long unsigned int pause = 25000;

boolean lockLow = true;
boolean takeLowTime;

int pirPin = 3; //the digital pin connected to the PIR sensor's output
int ledPin = 13;
int outPin = 12;

/////////////////////////////
//SETUP
void setup(){
Serial.begin(9600);
pinMode(pirPin, INPUT);
pinMode(ledPin, OUTPUT);
pinMode(outPin, OUTPUT);
digitalWrite(pirPin, LOW);
digitalWrite(outPin, LOW);

//give the sensor some time to calibrate
Serial.print("calibrating sensor ");
for(int i = 0; i < calibrationTime; i++){
Serial.print(".");
delay(1000);
}
Serial.println(" done");
Serial.println("SENSOR ACTIVE");
delay(50);
}

////////////////////////////
//LOOP
void loop(){

if(digitalRead(pirPin) == HIGH){
digitalWrite(ledPin, HIGH); //the led visualizes the sensors output pin state
if(lockLow){
//makes sure we wait for a transition to LOW before any further output is made:
lockLow = false;
Serial.println("---");
Serial.print("motion detected at ");
Serial.print(millis()/1000);
Serial.println(" sec");
digitalWrite(outPin, HIGH);
delay(50);
}
takeLowTime = true;
}

if(digitalRead(pirPin) == LOW){
digitalWrite(ledPin, LOW); //the led visualizes the sensors output pin state

if(takeLowTime){
lowIn = millis(); //save the time of the transition from high to LOW
takeLowTime = false; //make sure this is only done at the start of a LOW phase
}
//if the sensor is low for more than the given pause,
//we assume that no more motion is going to happen
if(!lockLow && millis() - lowIn > pause){
//makes sure this block of code is only executed again after
//a new motion sequence has been detected
lockLow = true;
Serial.print("motion ended at "); //output
Serial.print((millis() - pause)/1000);
Serial.println(" sec");
digitalWrite(outPin, LOW);
delay(50);
}
}
}

[soundmotor]

I like the idea, effort and creativity here. Did you try adjusting your cat's diet too? Sometimes changing brands is all it takes. The other is the litter. We use one of the bargain brands that comes in a big yellow 35 lb. bucket with blue or red top. No smell, even if we miss the cleaning schedule. That's the other thing, clean it more often. Now, if your cat is regularly going out on stewed mackerel & chorizo binges, none of the above may help.

;-)

[mailmam71]

I switched to shredded paper for kitty litter and it works great, I can clean my litter box everyday. I simply sprinkle baking soda on the bottom of the box and put the shredded paper in. At first I was hauling paper home from our coop but the bags were flimsy and would break, creating a big mess. I finally invested in a good shredder and the bulk mail and newspapers provide me all I need. I didn't like using clay litter as it doesn't break down, much like baby diapers in the landfill, and the biodegradable litter was pretty expensive. I'm solving two problems with one solution. About once a month, I wash the litter box.

[skybondsor]

I am so confused about why you glued the bottom of the food container to the lid. Don't you want air to be able to escape through the flap?

[astilly]

skybondsor: You are right, I wasn't clear about this in write-up. Will add some more detail. I cut a rectangle out of the downward-facing side of the container for the air exhaust. The closed top and sides of the container keep rain from possibly coming in through the duct. Gravity prevents rain from getting into the open bottom side. Will add some text details to the photos.

[skybondsor]

Ahhhh that makes sense. Thanks for responding!

[marxdarx]

Air does escape. It's just a flap. It prevents small animals and most larger bugs from entering the whole system. She basically duplicated what you would see in the kits she refers to.

Awesome Idea I think!

[skybondsor]

I understand the flap cut-out on the lid, using the zip-ties as a hinge of sorts. But why then cover that apparatus with the bottom of the food container? Wouldn't that prevent air from escaping?

[bstevenson1]

Assumably that glued on "bubble-cap" kind of thing has a hole cut out on the bottom to allow the air to escape.

[astilly]

Yes, exactly!

[PinUpRetro]

Cat boxes don't smell if you change the litter frequently and clean the litter box. Also depends what you're feeding the cat. Cheap ash-packed cat food will make their poo smell.

Or you could just toilet train like I have! :)

[DeliciousMystic]

how hard is it do toilet train? can old cats learn? do you have any good links or tips and tricks?

[astilly]

We tried the "City Kitty" system of toilet training prior to this ventilation system, with the careful cycle of adjusting them to get comfortable with perching atop the bowl, and all hell eventually broke loose.

We have friends who had success with it, so perhaps we just didn't have the right touch. Nevertheless, the potty training device blocks the toilet from normal human use for months on end, which is no fun for small apartment dwellers.

[PinUpRetro]

The one we used 'Litter Kwitter' is easy to pick back up off the toilet when you want to to use. We only have one loo in our house and had no issues. It's worth not having to change litter ever again to have a few weeks disruption

[PinUpRetro]

Depends on the cat. One of our cats picked it up straight away - lady (her daughter) is a dunderhead and took a bit longer.

Age is irrelevant unless it's a cat too old to balance on the seat. Pregnant cats shouldn't be toilet trained either (nursing either - just in case on of the kittens is attached to a nipple!) obviously kittens shouldn't be toilet trained for obvious reasons.

I used the Litter Quitter. But I guess you could try and make something similar.

Tips: move their litter tray into the bathroom - make sure they see it and the door is always open.

When they've gone a few times (all cats have to have reached this stage - as with each stage) you can exchange their tray for the quitter (red stage) on the floor. Then when they've successfully gone in the put it on the loo. Sookie got this first time, lady took a little longer - we had to go back a stage with her.

Then change to Amber (see the pattern emerging): which still has room for litter but has a small hole in the middle - encouraging them to aim for the hole and sit more on the seat and not in the litter.

The green stage is similar to Amber except the hole is bigger.

It can take a few weeks if you have a lot if cats or some stooooopid ones. If we just had sookie it would have taken a few days to go though the stages.

Great thing about this is they love it - their poo disappears ANC they don't have to bury it, you don't gave to empty a tray - just flush, don't have to buy litter any more snd when I have a baby I don't need to worry about handling litter.

The litter quitter fits over the loo, but it's best to

[Eirinn]

Yes they do! But you don't notice it because you're used to it. I couldn't smell anything but my moms face went from :D -> D: when she visited. And we clean it often, use quality "sand" and food :)

[rtanner]

Ah ha. My brother reminded me that cats who don't bury will ALWAYS have a smelly litter box, like his cat. The ones that bury, if you use a scented litter like I do, can keep the smell at bay for a day or 2. This is likely why I don't have problems, since my cats bury religiously and I'm still scooping it every day.

[rtanner]

Actually, I'd have to agree with PinUpRetro. I'm in and out of my apartment constantly with school and work. So I'm always having multiple chances to get used to the smell outside of my apt before coming back in. Never once have I ever come in, when I regularly clean the box, and thought "gee, that actually smells".
For the most part I clean it every single day and use a scented clay-based littler, for multiple cats, that I change every 2 weeks. I have 2 cats who use it a LOT and both are fed a natural diet.
I've NEVER had a problem with smelly littler boxes, and it's not because I'm "used to the smell" since I frequently am not home and have visiters over as well. My mother-in-law is a real clean freak and even she never smells it when she visits. She'd tell me too, trust me...
The only time I do smell it is when I forget to clean it for a day or 2.
So yeah. Maybe it depends on the cat, but it's certainly not all litter boxes since mine and PinUpRetro haven't had that problem.

[PinUpRetro]

Cheers bud - same here.

I'm out all day at work and would have noticed a smell when I came through the door (I'm like a bloodhound for smell).

We have three cats so emptied poo out twice a day and changed the (clumping smell absorbing) litter every 5-7days depending on usage (in the summer they tended to addnutrients to the flowers).

My mum has all the subtley of a sledgehammer to the face and would say if it smelt too.

Diet isimportant too (just like with humans) - eat a bad fatty diet and your/their poo will smell.

[astilly]

rtanner and PinUpRetro: No offense, but my mom said she never smelled her cat's litterbox either, and the subject was a laughingstock amongst my friends and wife whenever we visited. It was less about the poop and more about the ammonia / urea stench: made by a stronger cocktail of the same chemical compounds that make up human body odor. Given the relatively recent advent of indoor plumbing, something tells me the human olfactory centers have a way of adjusting to compensate. At least you two have each other;)

[rtanner]

Well, since your mom never smelled hers either I doubt that she got used to the smell as well. It might actually be the litter you're using.
A while back I actually tried a different litter called "World's Best Cat Litter", hoping to move from the clay based brand I had. Turns out I got rid of the stuff the very next day because I came home from being out for just half a day and was able to smell the stench. The litter did nothing to mask the smell.
After going back to the clay based stuff I again don't smell anything when I come home. So I definitely know the difference which would mean my nose didn't get used to anything. I bet the type of litter has a lot more to do with masking the smell than people realize.
Why don't you try switching out and see if that makes a difference? I use Fresh Step, if you were wondering. :)

[Quester55]

As Humans, We tend to forget how Sensitive an Animal like a Cat or Dog can be to Sounds We don't Hear or Vibrations We don't Feel.
Consider how you'd feel if you started Hearing the Whirl of a fan or feel your Hair move in a wind where none existed before, Each time you used the Potty, Now Amplify that a hundred times, That's what your Cat is going through. You might try Switching the Fan from the Box to the Window, To Quiet things down a bit, As well as making a Diffuser at the Box-End to tone-down the Suction under the Hose outlet.

[astilly]

Yes, I definitely want to try the fan on the window side of the apparatus. It would be interesting to test how a CPU fan performs when it is drawing from the far end of a tube rather than a relatively open space.

As for cat sensitivity to noise, my two tomcats are completely fine with sharing the same box on my first prototype and don't mind the fan noise a bit. On my 2nd build, my mom's older, female Calico started crapping all over the apartment, which is what pushed me to use the Arduino / PIR sensor solution (see last step) to shut off the fan whenever she approached the box. An LED on the top of the box turns off to provide her a visual to confirm the fan is off as she approaches.

[Quester55]

I was with you up until this point. For those out there that need Portability, Don't Cut the Jumper/ Connector off, Instead, find an old Female Plug, Soldier it to the wires ( Check for polarity first ) then Glue plug to fan housing. Now if the Transformer ever quits, just simply unplug jumper & replace as needed.
This will help If & When you ever move to another house.

[astilly]

Nice suggestion! I totally agree this should be part of the idealized version of this project.

[babykidlet]

This is a great idea and would work fantastically.! My husband made something similar back in the 1980s and we have been using it ever since. What we did was cut a "mouse hole" shaped opening (cat size) through a wall of our house to the outdoors. Then we built and attached an enclosed plywood box to the house, over the mouse hole. It has a a piano-hinged side, kept tightly closed with a sliding bolt gate latch, that allows easy OUTDOOR access to the standard size cat box pan inside. We put weather stripping in and around everything to secure it against bugs and weather. For exterior venting, we cut a hole in the plywood and placed a Rotron "whisper" fan (used in computers and electronic devices) in the hole and covered it with screening. We covered the fan with an elbow and then a 10' piece of pvc pipe that goes straight up the side of the house. The fan draws the stinky air out of the box and up the pvc "chimney," and his type of fan is quiet so that it doesn't disturb our kitties. Nobody has EVER smelled cat box at our house, and if you keep the mouse hole small, no bigger than kitty bodies, it doesn't affect your utility bill. It's a one-day job that saves you so much time and frustration! Paint a couple of mice at the hole and, voila!

[Madrigorne]

...another project ...
dang my list is really long

[5Volt]

Like it, +1 for the contest.
I no longer keep cats like I used to when I was a kid (they have the nasty habit to die after a while) but one of the things i remember is the litter-box smell, huh!
Alessandro

[Treknology]

Yeah, strange thing that. Cats seem to last about 20 years and then it's all down hill from there.