I've never used any type of air pressure system to unclog drains, but I've quite successfully used water balloons made specifically for this purpose.
The water balloon comes in various sizes (such as 2", 3", 4", 6", etc.). The balloon is made of very thick rubber, and is elongated. For instance, one for a 4" drain would be approximately 3.5" in diameter by about 6" long. It has a garden hose female fitting on one end, and an outlet hole in the other end. You attach the balloon to your garden hose, stick into the top of the drain at least half way, turn the water on, but not full force, and since the outlet hole is small, the balloon will blow up and expand inside the pipe to prevent water from flowing backwards. The water pressure is then foced into the drain pipe to unclog it. I've used these many times and have found that the type of clogs that I've gotten sewer and storm drains usually blow in 10 seconds or so. And I don't open the faucet all the way, just enough to get enough flow to blow up the balloon. I've read some of the stories about air pressure into clogged drains, and I can understand how those problems can happen, but I've never had a problem using these water balloons. I just don't believe I have to build up much pressure to blow out the clog. An air compressor is probably blowing in about 90 psi, but the hose pressure is probably a fraction of that since I just open the valve a little bit for the balloon to do its job. I bought mine at a local plumbing supply house, and I tried to google them to find them on-line, but couldn't find them. So if anyone is interested, let me know and I'll see if there's a brand name written on the balloons. Tom
