Leaky joints separate a successful plumbing job from one that doesn't meet expectations. If not sealed properly, areas where pipes or fixtures meet could produce an annoying drip or worse. Both plumber's dope and plumber's putty help provide watertight seals, but each is used for a different application.
Pipe dope, or plumber's dope, are slang terms for pipe-joint compound. The product comes in a jar and is the consistency of thin mashed potatoes. Pipe dope doesn't harden; it stays pasty, never becoming brittle or flaky. Those properties make it fairly easy to apply and ensures that the material fills all the voids created by threaded pipes. Pipe dope comes in two formulations: one for plumbing fixtures and one for gas or propane fixtures.
Using Pipe Dope
Equipped with an applicator, pipe dope brushes onto the male end of a pipe fitting. Apply it just before screwing two pipes together or before attaching a pipe to an elbow or similar joint. Coat the threads with a liberal amount of dope applied evenly across the fittings. Any excess will ooze out and can be wiped away. Once hand tightened, finish with a few turns using a pipe wrench.
Plumber's putty is malleable, thick and shapes with ease. The putty is made with mineral and vegetable oils, which help it stay flexible. Like pipe dope, plumber's putty doesn't harden or dry out, and it won't shrink or crumble. Putty is not made to coat pipe threads. Instead, it is used to seal flanges, like the one on a drainpipe where it meets the sink. Putty is also used to seal the space where a faucet meets the sink. Plumber's putty will not stand up to water pressure, so it acts more as a barrier that prevents water from leaking behind a fixture.
Using Plumber's Putty
Work a ball of plumber's putty in your hands to soften it up, then stretch the material into a long, snake-like form. Press it into place on the flange or fixture, and tighten the piece into position. Excess putty will squeeze out of the joint and can be put back in the jar for later use.