This device will automatically add water to your pool when it gets below a specified level. It does this all for under $15. By having a device fill the pool to a specific level, you can avoid wasting water by overfilling.

Step 1: UPDATE: VERSION 2.1 Cross Section Added for Stability

After version 1.0 kept falling over in the water, I added a cross section for stability. I spray painted the PVC Black to help protect it from the sun. It also makes it look much more finished.

Step 2: Materials

You Will need
Materials:
(1) Toilet Tank Fill Valve
(1) 3/4" PVC Pipe (At least 2 feet)
(3) 3/4" PVC 90 degree Elbows
(1) 3/4" slip fit to 1/2" threaded reducer
(1) 1/2" threaded coupler
(1) hose threaded to 1/2" reducer (I would recommend using a brass fitting, as it is much more durable. The rotating part tends to pop off of the PVC ones.)
(1) AquaMend Underwater Repair Epoxy Stick
(1) Teflon Tape
(1) PVC Pipe Cement
(1) 3/4" PVC 4 Way Cross Section***
(2) 3/4" PVC End Cap***
Tools:
PVC Pipe cutter (or saw)
Groove lock pliers

***Please see UPDATED section for picture of 4 way pipe fitting and end caps

Step 3: Cut the Vertical Piece

Cut the vertical piece of pipe that will hold the entire assembly low over the side of your pool.

Step 4: Add Elbows to Vertical Piece

Add two of the 90 degree elbows to the vertical piece, facing opposite directions.

Step 5: Epoxy Toilet Valve Into 90 Degree Elbow

Take the AquaMend epoxy out of its tube and cut off approx. 1 inch. Knead it together until a uniform color is achieved. Mold it into a string, and tear it in half. Set one part aside, and roll the other out, using the tube as a rolling pin. Get it long enough to wrap all the way around the threads on the valve. Wrap it on the threads and insert it into the tube as far as it will go. Use the second part you set aside earlier to form a nice, graduated seal on the pipe. Smooth this out with your fingers. Allow to harden for 1 hour before continuing.

Step 6: Cut 2 Shorter Lengths of PVC Pipe

Cut two lengths of pipe around 6 inches each. Insert one into each of the 90 degree elbows on the vertical (long) piece.

Step 7: Assemble the Coupler

Take the the 3/4" Slip Fit to 1/2" Threaded Reducer. Wrap the threads in teflon tape, making sure to wrap the tape in the same direction you will be twisting the piece into the coupler. Repeat for the hose threaded to 1/2" threaded reducer.

Step 8: Attach Hose Coupler Assembly

Attach the Hose coupler assembly to one of the short pieces of pipe on the Vertical pipe.

Step 9: Attach Toilet Valve to Vertical Assembly

Attach the toilet valve to the short pipe on the Vertical assembly

Step 10: Test Fit in Pool

Place the whole unit in your pool, and check to see if it sits around the right height. Connect it to your hose, but DO NOT turn the water on or it may come appart because the PVC has not been cemented yet. The valve is adjustable, as well as where the float sits, so make sure the float sits about midway in the water.

Step 11: Cement the PVC Together

If the test fit is the right size, go ahead. If it is not, either cut the vertical piece shorter, or cut a new longer one. Cover your work surface with towels or newspaper to prevent getting cement on it. Remove the joints one at a time and apply glue to the end in a circular motion. While inserting the pipe into the fitting, twist the pipe a 1/4 turn. Hold 30 seconds and wipe off excess cement. Repeat for remaining joints. Allow to dry for 2 hours before continuing.

Step 12: Test and Adjust in Pool

Take it out and place it in your pool. Connect the hose and turn the water on. Adjust the height of the valve and location of the float until the water shuts off.