Alcohol and salt works best, IMHO, but the key that people don't say is to use Kosher Salt. It is much coarser, and pointy and jagged. Its purpose is to be an abrasive inside your pipe, so put the salt in, then fill it with alcohol. 91% or 99% (gotta ask a pharmacist for that usually). 70% really does not work. You can use drinking alcohol such as grain alcohol (95%) but that gets quite expensive fast. Shake vigorously.

Acetone I hear works well too, but I have no first hand knowledge with that. I've also used the hot/boiling water method, and comparatively, that just doesn't work.

Also, I don't know why you want to clean your piece after ever use or two. I'll agree, a clean piece is the best, but only a bong needs to be cleaned everyday. Pipes get full of resin and its a good thing. It makes the smoke a lot smoother, and helps out in times of shortage (although that is the nastiest thing you can do) and helps catch any ash that pulls through or anything. It doesn't trap THC out of the smoke, besides what would normally be condensed on the walls of the pipe anyway. But if you are smoking anything with water, thats gotta be cleaned everyday. Not just a water change either, but alcohol and shit. Keep is looking brand new, and it tastes awesome. Bong water is nasty. Also if it's as clean as brand new, you can use hot water, which is a treat. Give it a shot before you knock it. It isn't "less thick" or whatever you guys will say. Just try it.:thumbsup:

Tl;dr: 91-99% isopropyl (rubbing) alcohol + kosher salt + enthusiastic shaking.