One mistake I've seen others make is putting a ball valve before the ball-lock fittings. This is unnecessary as the ball-lock fittings are quick-disconnects and stop any flow when removed from the posts.
Initially, I had planned to use 3/4" PVC pipe for the "nozzle". It worked fine for cleaning the kegs but seemed a little tight for the carboys. The neck of the carboy is pretty narrow and, because of the powerful pump, the carboy would begin to fill with water. I removed the 3/4" PVC pipe and replaced it with 1/2" copper.
The black fitting shown is a flexible rubber pipe reducer (4 inch to 3 inch). The 4 inch side fits nicely around the opening of a corny keg. (note: see update below...)
Some notes on use...
I use about 4 tablespoons (about 2 ounces) of PBW in 5 gallons of water. (Much less than the 1 to 3 ounces per gallon that 5 Star recommends.) This will begin to foam if the water is cold. (PBW does not foam as much when hot.) To reduce the foaming, start with hot water or you can eliminate the foam by squirting a dropper full of foam-control (Fermcap-S) into the bucket. As the pump runs, the water will heat up. With air and water at about 70F, the water temperature reached 130F after running for 90 minutes.
Doctor Scott's version:
Doc's version has some quick-disconnects so that different attachments can be added to the pump. He's also got a second set of ball-lock fittings that he can hook to a faucet or hose and rinse the cleaner from the keg posts and dip-tubes.
Tasty McDole's version:
Tasty included a little platform on his version to support the keg (instead of using the bucket's lid like I did). His platform is made from a cutting board. I'm not sure if he cleans carboys on it (I believe he uses conical fermenters) but it looks like you could throw a carboy dryer on the platform too.
Since building this I've come across another version... The pictures below were posted by "atfan" on The Brewing Network's forum. It looks like he didn't use a flexible reducer like I did and just made a bigger hole in the bucket's lid. I like this better than mine as it's a little simpler and the keg will always stand vertically (mine tends to lean a little bit). I also like the use of a bucket dolly. Nice!