Bathroom Sink Plumbing Tips
With bathroom sink plumbing there are three things to consider; a supply line, a waste line and a vent line. The supply line supplies the water with pressure. The waste line uses gravity to drain away waste and the vent line is attached to the waste line, but carries gasses upwards allowing ventilation to help the waste to flow downward. But first, find out the local code requirements!
Bathroom Sink Plumbing, Supply Line
Water is supplied under pressure from the supply system. The water goes through a main shutoff valve with a meter. Then it divides, one supply going to the hot water heater and the other for the cold water supply. The pipes for bathroom sink plumbing also have shutoff valves so the water can be cut off when you want to work on the faucets.
Your supply stub outs may already be protruding from the wall where you plan to install your bathroom sink. If so, your bathroom sink plumbing job will be fairly simple. If not you will have to ascertain where your water supply line is. It is not too difficult to find if the bathroom sink shares a ‘wet wall’ with another bathroom or kitchen (back to back).
If not, some people turn on the faucets in the surrounding parts of the house and use a doctor’s stethoscope on the walls to detect the sound of running water. Once you have detected the water supplies for both hot and cold water, you’ll have to remove a section of drywall. After cutting the pipes to insert T-pieces, if the pipes are copper, many plumbers stuff white bread into the cut ends to absorb any dripping water while they solder the joints. When the water supply is turned back on it will dissolve and be flushed away. Now you can install your pipes, and solder on elbows and stub outs to protrude through the dry wall when you replace it, after you have checked for leaks. Make sure the stub outs are long enough to install the shut off valves and give you enough room to work comfortably with the rest of your bathroom sink plumbing.
Most bathroom sinks have two faucet holes on 4-, 6- or 8-inch centers. The wider types are meant to receive a split-set faucet, with faucet handles separate from the spout. The 4- or 6-inch holes can be used for a center set or a single-lever faucet. Install the faucets with the flexible water supply hoses to the sink Then install the sink and attach the flexible water pipes to the stub outs protruding from the wall, as per manufacturer’s instructions.
Bathroom Sink Plumbing, Waste and Vent Lines
In the same way as with the inlet pipes, you will have to find the waste pipe if the drainpipe is not already in position below the sink’s inlet pipes.
The waste line uses gravity to drain away waste and the vent line is attached to the waste line, but carries gasses upwards allowing ventilation to help the waste to flow downward. You need to identify both waste and vent pipes.
They are usually the same diameter, about 1¼ to 4 inches, and nowadays they are usually of heavy-duty plastic, or neoprene. You can distinguish them by looking at the joints. The vent pipes use abrupt changes and sharp corners, T-pieces, while waste pipes have slow sweeping turns and special, flowing T-pieces. Assuming that your bathroom sink plumbing is fairly close to other installed bathroom fixtures, you will be able to link to the existing DVW lines. You need to refer to your local code requirements for pipe diameters/distance from main waste pipe.
Remember to use the slow bend joints for the waste pipe, and the waste pipe itself should slope downward to meet the main stack. The vent pipe is a continuation of the waste pipe, going up behind the sink inside the drywall, then turning to meet the waste stack higher up. The vent pipes should link up with the main waste/vent stack as least 6 inches above waste pipes from any other fixtures.
Remember to anchor the drainpipes as well as the supply pipes to blocking between the studs in the drywall. The drain fitting in the hole in the sink should be have plumber’s putty or silicon sealer underneath, where it fits into the hole, and below the sink a rubber gasket is pressed against the bottom of the sink by a brass washer and a nut. This should also be caulked to ensure that the whole fitting is watertight. Screw in the top section as far as possible, then tighten the nut below with a pipe wrench, so that the whole fitting is sealed nice and tight. Now you can install the trap and connect up with the drainpipe protruding from the wall. Now when everything is tidied off, and there are no leaks, your bathroom sink plumbing is done.
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