Teflon tape is an absolute essential for most plumbing projects. Its physical composition allows it to fill pipe threads and fitting threads with a sealant that will prevent water from leaking through the thread connection. However, the biggest problem with Teflon tape is that if it is not applied correctly to plumbing threads, then the fittings could leak. If you have a leak or drip in your plumbing fittings, then you should consider the use of Teflon tape to stop the leak.
In order to know whether Teflon tape will stop a water drip, you must first determine the type of fitting that is dripping. If the fittings are slip fittings that are glued together, then Teflon tape will not help. These type of leaks must be repaired by cutting the PVC pipe and replacing the fitting. If your pipe fitting is threaded at the place of the leak, you may very well be able to stop the drip by unscrewing the pipe joint and replacing the tape. Threaded pipe fittings come in a variety of materials, such as PVC, steel and even copper. Teflon tape will work on any of these threaded fittings.
Teflon tape comes packaged on a small roll that resembles a roll of electrical tape, except that the tape is white, 6 mm (1/4 inch) wide and does not have a sticky surface. The tape resembles thin vinyl, similar to plastic. Placing the Teflon tape around a threaded fitting is the single most important step in stopping a drip. If you are placing the tape on an old threaded fitting, making sure that the threads are clean will ensure a tight seal. Use a small brass toothbrush-size brush to clean the fitting, making sure that no old residue remains in place. When applying the new tape, wrap it counterclockwise so that when you rethread the fitting, the tape end won't come unwound -- you will thread the fitting in a clockwise direction. Stretching the tape tightly will help ensure success. You may wind several passes onto the fitting, but don't go over four passes. If the tape is too thick, then you won't be able to thread the fittings together.