For a quick fix on leaky pipe joints, use two-part epoxy putty. Slather it on liberally. This fix may not last long on a water supply line that has a lot of pressure going through a galvanized pipe, especially if there's rust on the pipe. But drainpipe joints aren't subjected to force and this may be all you need to do to avoid a plumbing call.

The pipe must be dry for the putty to adhere, so turn off the water to the sink or tub, and then apply the putty following the manufacturer's instructions. Wrap the puttied joint with electrical tape before it dries; and then after it's dry, turn the water back on. If you still have a leak, get out the phone book. A plumber will have to repair the joint.