About 7 years ago we installed the sink in this bathroom.
Washing machine draining back into sink.
The reason you want to have the drain pipe slightly larger is to allow for ventilation.
The sink and the washer use the same discharge pipe.
In either case you probably have a clog in the drainage pipe after the two combine.
The plumber has been here twice and installed a vent in the pipe but it still happens.
I live in a raised ranch.
Drain hose from washing machine pushed too far down into the drain pipe.
The toilet and shower are backed up to the laundry room.
Increasing the inside diameter of the drain pipe to 2 might help more.
If the sink doesn t back up on its own when you do the dishes or run the faucet the clog is probably deeper in the pipes and only responds to the large volume of water being drained from your washing machine.
The outside diameter of the drain hose attached to the washing machine is 1.
Leave any drain cleaner time to work then repeat the drain test from step three.
If you re going to connect the washing machine drain hose to the sink drain before the p trap the entire drain including the trap needs to be constructed of a 2 inch pipe.
Both drains may empty into a toilet waste line and be.
How to fix the problem.
If the washing machine drains push it back into place but check as you do so that the hose isn t becoming pinched.
The output from a washing machine is under pressure and a standard 1 1 2 inch sink p trap assembly is too small to handle it.
This means that when the washing machine starts releasing water down the drain that is connected to the sink drain the air will actually be trapped inside the main drain pipe.