The Spruce / Kevin Norris
Bathroom sink plumbing is easy to understand and simple to repair.
There are very few parts, and most parts are accessible inside the sink cabinet.
All bathroom sink plumbing parts are divided into either water supply parts or drainage parts.
The Spruce / Kevin Norris
Learn about bathroom sink plumbing, including water supply parts like supply tubes and drainage parts like tailpieces andP-traps.
Most have an oval, football-shaped handle that you turn to open or end the valve.
They are seen in pairs: one valve controls the hot water; the other controls the cold water.
The Spruce / Kevin Norris
Many shutoff valves use compression fittings, so they can be installed onto the water pipes without soldering.
But you will have to turn off the water to the house to replace a shutoff valve.
They are connected to the bottom of the sink faucet and shutoff valves with attached nuts.
The Spruce / Kevin Norris
These supply tubes sometimes fail, and it’s not uncommon to have to replace them.
Underneath the nut is a tapered plastic washer that creates a watertight seal.
P-Trap
TheP-trapis a curved drainage pipe under the sink.
The Spruce / Kevin Norris
The P-trap’s curve is designed to hold standing water.
The standing water prevents sewer gasses from rising from the sink drain.
The bottom of the U-bend is always filled with water so that gasses can’t pass through.
The Spruce / Kevin Norris
P-Trap Adapter
The P-trap adapter connects the P-trap to the home’s drain pipe.
For the water supply, you’ll need two water supply tubes and two water supply shut-off valves.
Bathroom sink plumbing parts are mostly standard-sized for drainage pipes: 1-1/2 diameter.
The Spruce / Kevin Norris
Supply lines on a bathroom sink should be 8-1/4 inches high.
They should also be higher than the bathroom’s drain outlet.
