How to Clean Out a Bathroom Sink P-Trap

Begin by removing all items from the cabinet under the bathroom sink to create a clear and accessible workspace. Place a medium-sized bucket directly under the U-shaped bend of the P-trap assembly. This bucket is essential for catching the water and debris that will spill out when the trap is removed. For added protection against spills and splashes, lay down a few old towels or rags on the cabinet floor around the bucket.

Identify the P-trap, which is the U-shaped pipe under the sink. It is connected at two points by large threaded nuts, known as slip nuts. One connects to the vertical pipe coming down from the sink drain (the tailpiece), and the other connects to the horizontal pipe going into the wall (the trap arm). Grasp one of the slip nuts with a pair of channel-lock pliers. Turn the nut counter-clockwise ('lefty-loosey') to break it free. It may require firm, steady pressure. Once it's loose, stop. Repeat this process for the second slip nut. Do not unscrew them completely at this stage.

With the bucket correctly positioned, finish unscrewing the now-loosened slip nuts by hand. As you undo the final threads, expect some water to begin dripping. Support the P-trap with one hand as you unscrew the second nut. Once both nuts are free, carefully lower the P-trap, allowing the captured water and accumulated gunk (hair, soap scum, etc.) to drain completely into the bucket. Wiggle the trap gently if it feels stuck.

Take the detached P-trap to a utility sink, or use an outdoor hose for cleaning. Use a flexible bottle brush to scrub the interior walls of the trap, dislodging stubborn buildup. A straightened wire coat hanger with a small hook bent at the end can be effective for pulling out large clumps of hair. After manually removing the bulk of the debris, flush the trap with hot, high-pressure water to wash away any remaining residue. Inspect it visually to ensure it is completely clear. Also, use a rag to clean any gunk from the threads of the slip nuts and the trap itself.

Before reinstallation, carefully examine the tapered slip-joint washers that sit between the pipes and the slip nuts. If these washers are cracked, brittle, or flattened, they will not create a reliable seal and should be replaced. Position the clean P-trap back in its original alignment, ensuring the washers are correctly seated with their tapered side facing the pipe end they are sealing against. Slide the slip nuts into position and begin tightening them by hand, ensuring they are not cross-threaded. Hand-tighten both nuts until they are snug.

After hand-tightening, use the channel-lock pliers to give each slip nut a final quarter-turn. This provides the necessary compression for a watertight seal without risking damage. Do not apply excessive force. Place a dry paper towel on the cabinet floor directly under the P-trap; this will make even the smallest leak immediately visible. Turn the sink faucet on and let cool water run for at least a minute. Watch both slip nut connections closely for any drips. Then, stop the sink drain, fill the basin about halfway, and release the stopper to test the connections under the pressure of a large volume of water. If a leak appears, try tightening the nut slightly more. If it persists, disassemble, check washer alignment, and re-tighten.