I was walking in Wal*Mart one evening and went past the pet asile. I picked up some inexpensive aquarium supplies with the intent of putting together my plant watering system. I also went to the hardware asile and picked up a 24 hour light timer. In the end I had to go to a pet specalist store to get the valves that I needed to get it to work.
Here is my supply list
25' Airline Tubing ($2)
4 Gallon Bucket ($2)
Aquarium air pump ($10) - I got a dual line mode, beefier the better (not pictured in the instructable)
24 hour timer ($4) - Originally I used a 1 hour timer, but I found a 30 minute timer that worked better
Lee's Airline Control Kit ($4) - Cat no. 14103 - This is the perfect set for this project - it contains 4 Tee junctions and 5 valves. The valves are inline and all plastic.
Check Valve (Free) - This should come with your pump and is very important for safety (not shown in pictures)
Step 1: Prepare the junction and valve
Then take the tee junction and press the valve body on to the perpendicular part of the tee.
If you have a different type of junction or inline vavle you made need to fashion a small length of hose to join the tee and the valve - it'll work just fine.
Step 2: Attaching the pump and line
IMPORTANT: Even though it is not pictured, install a check valve close to the pump. This is a important safety point, considering that you are dealing with water and electricty - they don't mix very well!
Step 3: Run the line to your plant
Try and keep the line from the bucket to the plant as short as possible - dips in the line between the bucket and the plant will reduce the efficently.
Step 5: Finishing up
The valve works on suction, as the air rushes by in the tee fitting it will suck water from the valve and that water will be pushed along through the outgoing line to your plant. When it is on it sounds like a coffee pot brewing.
Adjusting the valve can be tricky - if the valve is open too much air will just escape and make bubbles in the bucket, but you want to get enough water to your plant. Mine are adjusted down pretty far - after all 30 minutes of a drop of water a second is actually quite a bit of water. I "calibrated" mine with a measuring cup.
Maintaining the system is minimal, just keep the water above the 1/2 line and you'll be okay. Also, keep things from floating around in the bucket. Check the lines to your plants every once in a while, the water can come out with a surprising amount of force - I found when my bucket will totally full the line would spit water over the edge of the pot.
Note: The photographs in this instructable were setup - the one in my office actually follows all the steps :)