Rain Tank- From Paper to Reality

Introduction: Rain Tank- From Paper to Reality

It started with some simple data collecting after I moved into my current house. After realizing the amount of rain that was being wasted (mainly under my house) I had to act. I sketched a few rudimentary ideas on a napkin at work but soon became distracted by life (a few kids, leveling the house, adding gutter diverters away from the house, etc.)

The drive to design and build an efficient rain collections system resurfaced a few months ago and this time I wouldn't let go. So follows is my rendition of rain harvesting:

Step 1: Ingredients

1. Rain

2. Roof/Gutters

3. Water Tank (NTO tanks has several selections at a reasonable price with surprisingly quick service)

4. First flush system (After designing my own I found Rain Harvest Systems with an almost identical system)

5. Numerous schedule 40 PVC pipes/fittings (see pictures)

6. Just see pictures for the other stuff.

7. Basic tools (i.e. saws, glue, tape, markers screw drivers, outdoor screws, drills, etc.)

Step 2: First Flush

The idea behind a first flush is to separate the general gunk that comes off your roof, that most gutter systems miss, from your collection tank. The amount to divert to the first flush depends on the size and contamination of your roof. For my test roof : Approximately 700 sp. ft; a 18 gallon first flush is more than adequate (see the website for resources)

The company Rain Harvest Systems has a complete kit (actually multiple kits... I really wish I had found this company earlier in my designing and building)

Follow their instructions or use their designs as inspiration to build your own first flush system. In the end it doesn't matter which you do. The length of 3" or 4" pipe required for an sufficient flush would take up more space and would be close in price to a three foot section of 12" pipe added to this company's 12" to 3" reducer. This was a case of "They got it figured out with a product at a reasonable price. Guess I should buy it."

Step 3: Floating Intake Filter and Outlet

The bottom bulkhead for my tank was 2". So everything bought was to attach to this piece and then size down to a garden hose connection on the outlet end (separated by a gate valve) and a 5/8 ID hose on the floating filter end


Fairly straight forward construction here:

Take your 2" threaded bushing and attach 2" to 3/4" bushing

Attach your chosen gate valve to your brass couplings with plumber's tape

Attach to 2" bulkhead using plumber's tape

Admire and eat pizza as celebration

Bloating Intake:

Be gluten intolerant

Eat gluten

Go to Museum of Tolerance

Floating Intake Filter:

Assemble another 2" threaded bushing with 2" to 3/4" bushing

Attach Brass adapter (5/8" to 3/4" threaded) to hose, tighten #012 ss clamp

Attach Nylon adapter (1/2" to 3/4" threaded) to hose, tighten #012 ss clamp

Attach 1/4" eye bolt to toilet tank float and attach to Nylon adapter end of hose (number of methods to accomplish this: 1- With fish line and about 6" of slack or 2- Place nylon barb through eye bolt prior to attaching hose)

Attach water bubbler to nylon end

Attach brass end to already assembled 2" threads

Lay tank on its side and attach to 2" bulkhead with plumber's tape

The idea behind the floating filter is to have it float a few inches below the surface (to avoid any floating contaminates) and to collect water above the bottom of the tank (to avoid sediment). If you're worried your tank will run dry then attaching some fish line to your float and the top of the tank would at least avoid sucking up the sediment. There are commercially available floating extractors/filters but the price is quite steep. (ex. Rain Harvesting Supplies) So spending $30-$40 is much cheaper.

Step 4: Overflow

The overflow is also straightforward. Just attach a P-trap to a length of 1 1/2" pipe (This is variable based on your tanks design. I had to extend past the taper of my tank to allow it's required height) then attach that to a 1 1/2" threaded bushing which then attaches to the tanks 1 1/2" bulkhead with plumber's tape.

Some thought did go into this basic design:

A P-trap is meant to keep In---In and Out---Out.

At the end of the P-trap attach a short section of 1 1/2" pipe cut at an angle (This allows any floating junk to siphon through the overflow and further increases the quality of your collected water)

The angled piece also raises the height to above the discharge end of the overflow so that gravity can do what it do.

The drain cap... I haven't yet determined how much use it serves at this time so I haven't installed it. Because I could only find a 2" drain and not an 1 1/2" drain, I would have to attach a 2" to 1 1/2" reducer to even use it. This seems a bit superfluous as I already have the P-trap in place.

Step 5: Final Attachments

The location of the tank was logically placed close to the test roof's gutter downspout (Why spend extra money on long sections of pipes?). As an added level of convenience for this location, there were several already level concrete stones here. For a tank with these dimensions 16- 1'x1' blocks provided a good footing. You will have to use your own discretion on this part... actually you're going to need to use your own discretion on all the remaining steps. This is not an exact science.

Tank Location:

Put it close and level to your downspouts (use concrete blocks, pour a pad, whatever you got)

Laying Pipe:

Attach the 3" T-piece (Since my Leaf Eater was located at the end of the downspout and the first flush below this I had to play with the required lengths of 3" pipe between connections. Ultimately make the final connection to the leaf eater and screw it in it's final location below the downspout.)

Rough fit all the remainder pieces to fine tune the length of pipes and rotation of the fittings

I settled with a 2' section of 3" pipe at a slight decline from the 3" T-piece (supported with a #072 ss clamp), a 3" elbow/90 attached parallel with the wall

Use the two 3" rubber couplings to fine tune the rotation of the 3" elbow/45 to locate the position for the bulkhead installation on the tank


Use the rough in detailed above to locate and mark the placement.

Remove rough in and screw hole with 3 1/4" hole saw

Clean edges and attach bulkhead with rubber gasket on inside of tank.

Attach 2" threaded bushing to bulkhead

Attach 3" to 2" reducer to bushing


Attach 2" threaded bushing to bulkhead with short length of 2" pipe

Attach 2" elbow/45 to length of 2" pipe (this varies based on height of tank)

Attach 2" elbow/90 to 2" elbow/45 to end of 2" pipe

Finally attach diverter to the short 2" pipe inside tank

(The idea behind the diffuser is to avoid disturbing the sediment in the bottom of the tank)


Using the two 3" rubber couplings attach the 3" elbow/45 with short section of 3" pipe to the tank and to the downspout

How to construct this last bit:

During the rough in detailed above you end up eyeballing the approx. length of each section

Then attach the piece making sure that the elbows are still going to line up

Then once these pieces are to the length they need to be

Cut them in half and use the 3" rubber couplings to attach everything.

(The idea of course to allow for easy assembly, disassembly, and maintenance)

Step 6: Final Thoughts, Etc.

I believe this build went surprisingly well, considering I have no plumbing experience. Total time to build once supplies were in hand: Two days (that's 4 hours [There's a two hour window where both children are napping and their bellies are full]) It almost took 2 hours in Home Depot just finding all the parts. This part will go much faster with the next tank. I am now just waiting on it to rain so I can fully test my system.

Total cost: ~$930

Tank: $438 (www.ntotank.com) [includes shipping]

First Flush: $262.61 (www.rainharvesting.com) [includes shipping]

Fittings: $209.01 (Home Depot / Lowes)

Filters: $38.86 (Amazon / Lowes) [Actually bought 4 bubblers, so closer to $6 without shipping]

Additional Fittings/etc: 15 [To correct the little flub of getting the wrong connection size]

Additional reading is attached (again... wish I found this before I invested so much time in my design. Could've just borrowed everything from the different resources)

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    7 years ago on Step 6

    There are multiple options that would work. As I may have mentioned already, this tank is my prototype design. There are several redundant, or otherwise unneeded, features. I wanted my prefabricated holes to face forward. This lead to the natural question to either deliver the rain to the front of the tank and have a multipurpose pipe for both delivery and overflow of rain (as your question seems to be asking) or cut a hole and place a bulkhead in the back of my tank. I went with the latter option due to a combination of ascetics and supplies on hand at that point of the build. The top-front prefab hole then became the overflow with a p-trap at approximately the same height as my intake on the opposite side. Having a p-trap-like device on the intake side would work at lower flow rates, however higher flow would wash out any trapped sediment. This is why I use a first flush. I'm sure a "t" fitting on the intake side, prior to the tank, placed in a vertical position at a height between the overflow line of your first flush (or rain gutter) and maximum volume line on your collection tank would work as an overflow with only one entry point. I'm not sure how it would work to keep any further dirt from entering your tank. Perhaps in a horizontal position with a sediment filter on the downward part of the "T" with that then going to your tank. It would still function as an overflow once your water line in your tank gets above your "T" fitting (i.e. there would be a back flow, since gravity is the engine behind this system). Really no matter what you do (excluding using gutter filters then a first flush device and then multiple inline, gravity-fed filters) you are going to get dirt in the bottom of your first tank.

    My tank has been in use for over a year. There is a biofilm coating on everything inside my tank (no algae. I cannot stress that enough. No light penetrates any part of my collection system). There is a sediment layer less than an inch in depth (Again this is from over a year of use with absolutely no maintenance to any of the parts, no cleaning, no vacuuming). The only thing I have to do is clean the filter at the bottom of my first flush (the first flush has an "auto-reset" that drains itself after a rain, so every few rains I do need to clean the sediment that has collected in the bottom. Otherwise I increase the chances of this dirt being transported to my collection tank. Honestly I feel like this is the reason for most of the dirt that has found its way in my tank.)

    I have added a submersible pump that is kept afloat by small bike inner-tubes. This now allows me to transport my collected water further and faster. The intake for the pump is a few inches below the water line to avoid any potential "floaters" from clogging the pump. The water that comes out is not clear (meaning it has a slight discoloration to it) but there are no particles noted upon initial inspection and subsequent inspection (i.e. when the water has time to settle).

    In summation:

    My overflow and intake are approximately the same height.

    The first flush design handles almost all of any dirt prior to entering my collection tank

    The diffuser experiment minimizes turbulence to assure dirt stays at the bottom of the tank

    It is currently storming where I live so I cannot do this now, but I will attempt to take better pictures to better explain and, hopefully, answer any questions you may have.


    7 years ago on Step 6

    Howdy! I can't tell from the pictures, is the overflow higher, lower, or the same height as the intake? It seems to me that using a "t" fitting on the intake would work for overflow, and would keep any other dirt from flowing into the full tank, and save you the trouble of cutting one hole?


    8 years ago on Introduction

    Thanks for the reply! I'm just trying to learn as much as I can about
    rain water collecting, currently have only two 55 gallon barrels. I
    admire the engineering that went into designing those first flush
    systems, but none of them look like they hold enough water to do the
    job. I actually use the first 55 gallon barrel for the first flush, and
    the second barrel for clean water. I still use the dirty water for
    many applications that don't require pristine water, so it's not a total
    loss, but when I need clean water I pull it from the second barrel.


    Reply 8 years ago on Introduction

    It's not an exact science. My test roof happens to be quite clean. Try adding simple leaf guards (ex. GUTTER GUARDS) to your gutters. Add a Leaf Eater to your downspouts. The latter is mainly for any potential mosquitoes but its size is much smaller than my gutter guards. This of course further pre-filters my water prior to ever reaching my first flush system. Theoretically, a simple Sodium Hypochlorite treatment to my holding tank followed by a pass through carbon filters would bring my water to potable levels.


    8 years ago on Introduction

    I'm curious as to how you come up with 18 gallons to flush 700 sq ft of roof? If you took 18 gallons up to the roof, would it really flush all the dirt off the roof and down the gutter?


    Reply 8 years ago on Introduction

    No. 18 gallons thrown on the roof would not do anything.

    A first flush is nothing more than a wasted percentage of the surface area of whatever you're collecting from. My particular roof is 700 sq ft. There is nothing above it (i.e. no tree branches, power-lines, etc.) and I have fairly simple leaf guards on this gutter. This means nothing but the ordure from the occasional tired bird needs to be washed away. So only a small percentage (about 2.5%) of the initial raindrops collected across the entire surface area of this roof would be considered less than desirable for potable water (this being the ultimate goal from one of my roofs). At least 50 gallons of rain probably falls before my asphalt roof is through evaporating water from any excessive heat stores, before it is fairly saturated with water and before the gutters are full enough for the water to begin its journey to the gutters and the first flush system below.

    As detailed in this article this is my prototype. The filters need to be cleaned about every other rain or my auto-reset drains slower. There is some amount of sediment in my collection tank. This could be from having too small of a first flush, not cleaning out the filters in my first flush often enough, or just general inefficiencies... it's all part of the learning process. Of note, since I've begun cleaning my filters more often there has been no growth in containments in my tank.

    Oh and to answer your question about how I calculated the volume: go to several of the links I've embedded in my article. (Try "complete kit") There are also numerous other resources that I've read throughout the years that I just can't find again that went into my calculations. The pdf I've attached if very helpful (wish I had if before I started), Page 8 should be about first flushes.


    8 years ago on Introduction

    I'm curious as to how you come up with 18 gallons to flush 700 sq ft of roof? If you took 18 gallons up to the roof, would it really flush all the dirt off the roof and down the gutter?


    8 years ago on Introduction

    Nice project! You should add a photo of the finished tank to the intro step as the main image. You'll get more clicks that way :D