In every home we face the problem of cleaning the toilet, there are many products and devices which must be replaced every few months and do not achieve a complete cleaning. From pills to hang on the bowl to soap dispensers into the tank; they all use large amounts of some chemical very harmful for the environment that will go directly to the wastewater; they only remove a small portion of dirt but try to dissimulate it with an artificial aroma.

After trying some of these devices I've done my own invention, an automatic dispenser that is placed inside the tank. Mixes a small amount of disinfectant with the water every time that the tank is emptied. The disinfectant acts slowly on organic matter and also on calcium or other water impurities, dirt does not stick to the toilet bowl and there is not organic matter that can emit odors; we'll not smell anything, even not the disinfectant because very little quantity is poured. Works using the gravity force and has no moving parts so maintenance is null and the unit will last for years.

It has the advantages that performs an automatic cleaning without needing to touch manually additional devices; the disinfectant only must be replaced once a year or when we see that has lost power, that depends on the number of times that the water is dropped.

Although it is very effective sometimes also we have to scrub too much persistent dirt with the toilet brush, in this case we'll see that the dirt is not nearly stuck to porcelain and may be cleaned easily.

This is my own original invention that stands out for its simplicity and effectiveness, is very cheap to make and also to refill; has been tested for some time in my house and those of other friends; we have found that replaces successfully other devices and outperforms all others in every aspect. No problems have been found. Hope you find it useful.

Note that we do NOT have to make any extra hole in the cap or in the bottle.

There is also another version of this instructable for Spanish speaking people.

Step 1: Materials and Tools.

To build the device:

small bottle of soft drink (33 cl. or similar) with threaded cap.
a nylon tie, long enough to surround the bottle, over 20 cm (8").
a little piece of a synthetic duster.
a piece of semi-rigid plastic, about 0.5 mm thick, as high as the bottle and as wide as the diameter.

To fill a bottle of 33 cl, all volumes are approximated:

260 cc. (3/4 of the size) of hydrochloric acid
20 cc. Liquid soap (dishwasher or similar), it could also be window cleaner.
must be left free space, (1/8 of the size) filled with air for expansion and contraction.

In North America, maybe we'll find 12 fluid ounces (355 ml) bottles, in this case use 9 ounces of hydrochloric acid and one ounce of soap; and leave 2 empty ounces.

Tools:

scissors or other cutting tools.
heat gun or hair dryer.
highlighter to mark.
optionally, a kitchen scale or a volume measuring cup; although you can also mark approximately.

Step 2: Bottle

Look for a PET plastic bottle, transparent, thick and durable, with ergonomic design providing a flange that helds the nylon tie.

There are plenty of refreshing drinks served in small format, This is a small bottle of soft drink (33 cl. or similar) with threaded cap.

Mark the filling levels of each one of the components using a scale or a volume meter.

Put the bottle of 33cl in a kitchen scale and fill the bottle with water. Mark the levels at 260 and 280 grams. Empty the bottle after doing that.

When we do not have a scale or volume meter, we'll mark approximate levels to 3/4 of the volume and a little higher; the figure will give you an idea of the proportions.

Step 3: Cap.

We have chosen a bottle with threaded cap, that allows us to scale the closure of the bottle and leave it slightly open.

Take a synthetic duster and cut off a round piece larger than the cap with an additional 5 or 6 mm radius. We will keep this circle of cloth for using later.

I used the multipurpose duster of 36x40 cm. 6 units per pack; the most affordable found out there in the market.

Step 4: Hook.

Cut a piece of thick semi-rigid plastic. Should be almost as high as the bottle and as wide as the diameter.

Is preferred a very rough or corrugated plastic to allow adjust the position of the bottle; When the plastic is too smooth we'll do notches at the sides which retain the nylon tie as shown in the figure.

Next we'll fold this plastic to make a hook. Heat the plastic with a heat gun and fold it around a pencil or a piece of wood to form the hook shape.

Then attach the hook to the bottle with the nylon tie.

Step 5: Replenishment.

Fill it with most of hydrochloric acid, 260 cc., and some 20 cc, liquid soap or window cleaner. Leave an unfilled part for expansion and contraction. Close the cap and shake to mix.

This ratio of hydrochloric acid and soap gets a perfect cleaning and makes very little foam, if you put greater proportion of soap it will make more foam and also cleans pretty well.

Update 21-Jul-2015. I have found that the acidity of the hydrocloric acid is lost almost completely within a few months; Now I prefer to fill it with a higher proportion of soap and periodically clean dirt that is left in the bottom of the bowl applying a little gush of hydrocloric acid.

The hydrochloric acid is a strong acid that decomposes organic matter and also calcium and other impurities from water. Soap creates a slippery film on the porcelain that increases the exposure time to the disinfectant, in addition dirt will slide down. The tank water becomes slightly acidic, that is enough to decompose slowly calcium and other impurities from water and prevent fouling on the bowl.

Previously we had to clean the toilet so often with large amounts of highly aggressive chemicals, with this appliance the toilet will be kept always clean and only needs a small amount of product in the bottle that will be released dropwise every time that we empty the tank, refilling it every year or even later.

Remarks:

We must wear waterproof gloves whenever we handle highly corrosive products such as hydrochloric acid.
When we transfer liquids from one container to another we should place them over a large bowl to collect any accidental spillage.
And always we should work very close to a drinking water tap to allow us washing immediately when any drop splashes over us.
All toilet cleaners are based on acids. Never use bleach because if you mix it with ammonia from urine or hydrochloric acid will produce small amounts of highly toxic chlorine gas.

Step 6: Place the Duster Circle on the Cap.

Put the circle of cloth inside the cap, close the bottle and press to screw the cap on the duster.

The bottle should be slightly open, when we reach the bottom we'll unscrew less than a half of turn until feeling that the cloth touches the neck of the bottle but is not tight.

The cloth acts as a porous membrane that prevents the free flow of liquid. After little time running, the cloth is impregnated with soap and looks like a gelatin sponge; also the cap thread makes a lot of resistance to flow.

Step 7: Install the Device in the Tank.

We put the bottle in the tank. Be careful to position it in a place that does not get in the way of the mechanisms, buoy or discharge valve.

Is regulated according to the submerged depth; will expel much more cleaner when more immersed we place it.

In installations that I have in operation, initially we have placed the bottle as high as possible, as is allowed by the lid of the tank, being submerged only a third or fourth part of the disinfectant. Thus it is sufficient, the water is slightly acidified and cleaning is very satisfactory.

Some time later, after a few months, the solution will lose strength so we will dive the bottle a little and it will continue maintaining all of its cleaning power.

If there is a lot of dirt stuck in the bowl when we place the device, will go descaling with the passage of time, plus occasionally we'll scrub with the brush, after a few weeks the toilet will shine. We may help cleaning if we apply a little gush of hydrochloric acid under the rim and let it work its way down. Close the lid and let the cleaner soak in the bowl for some hours; after scrub with the toilet brush. We must be sure that the hydrochloric acid is applied only over the inner porcelain bowl and not on other parts, therefore avoiding the risk of damaging metals or chromed plastics.

Step 8: Operation.

When the tank is full of water, by the Archimedes principle, the bottle receives an upthrust equal to the volume of water it displaces, the duster lets water pass inside the bottle and the internal air is compressed to balance the inside pressure to the outside.

When emptying the tank, the bottle no longer receives the thrust of outside water, the weight of the disinfectant produces a small decrease in pressure in the bottle, the air expands and expels a few drops of disinfectant mixture through the cloth.

It is a cycle of two phases according to the filling and emptying of the tank.

In the fill phase water enters into the bottle, internal pressure will balance with the outside; once it is stabilized there is no more liquid flow because the duster and cap thread offer much resistance to the fluid flow.

In phase 2, when the tank is emptied the bottle ejects drops of mixture of water and disinfectant due to the weight of the liquid. Only a small quantity, the bottle can not be emptied out more because the surface tension of the liquid in the cap acts as a valve plug and seals out the air.

Step 9: Depth Is Related to the Volume of Disinfectant Expelled.

The volume of disinfectant mixture to be released at each cycle depends on the depth at which the device is attached.

Suppose the state 1 where the water from the tank reaches the level of the disinfectant h.

In state 2 we emptied the tank; the surface tension of the liquid acts as a valve plug and seals out the air; the internal pressure P2 is lower because the air supports the vacuum caused by the weight of the disinfectant, the interior gas expands and discharges a small amount of disinfectant.

We calculate the volume ejected by the law of Boyle-Marriot. We use as units cm and kg.

Initial data:

Vair1 = initial air volume, 50 cm3

R = the cylinder radius of the bottle, 3 cm

Variables:

Vair2 is the volume of air when the tank is empty.

Vd is the volume expelled

Equations:

P1 * Vair1 = P2 * Vair2

Vair2 = Vd + Vair1

By varying the depth h, 0 <= h <= 100%, we could calculate the volume ejected. Find the exact solution is complex, I prefer to immediately expose the already settled relationship and miss the deduction of theoretical formulas.

Result:

h = Vd^2 / 14 + 5.571023897 * Vd

Released volume of disinfectant is almost proportional to the percentage of submerged depth h; in our case will vary from 0 to 0.18 cm3.

Check the results.

Suppose the following cycle: in state 1 the water in the tank reaches the same level as the disinfectant, so that the pressure P1 = 1 kg / cm2.

Results are calculated in the limit points, 0 and 100%.

1- When h = 0 then Vd is 0. OK.

2- When h = 100%, then:

P1 * Vair1 = P2 * Vair2

1 kg / cm2 * Vair1 = (1 - ((0.280 kg - Vd) / pi / 3^2)) * (Vd + Vair1)

At each cycle our device ejects 0.18 cm3 of disinfectant when the water level is at the depth H (which coincides with the top level of disinfectant, 100%), OK.

Step 10: Disinfectant Concentration Varies With the Number of Repetitions of the Cycle.

When emptying the tank the bottle drops a small part of his contents.

When the tank is refilled then water refills the previously ejected volume and the cycle begins again.

In an real installation the process will be repeated hundreds of times, water will be mixed into the bottle and the concentration of disinfectant decreases; after several hundreds of cycles much part of the disinfecting power of the solution is still maintained.

Observe the graph above. It has been theoretically calculated for an initial volume of 250 cc. of disinfectant and 50 cc. of water; after about 900 cycles the disinfectant volume is half, has been replaced by water.