The downside of the tap idea is you either have to already have one or go buy one. Bread is nearly free.
[on edit] I just remembered another bread trick we used to use. When soldering copper pipe that won't quit dripping, stuff some bread inside the offending section of pipe, then sweat the joint. It's impossible to get a good sweat joint if there's any moisture inside. The bread flushes out after turning the water back on.
