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Why does a washing machine drain pipe keep overflowing even when there are no obstructions in the pipe?

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July 25, 2010 3:52PM

The washing machine is pumping out water faster than the drain pipe can handle. A trap in the drain pipe to which the washing machine hose is attached is required and that makes the water flow slower than you might expect. Having the washing machine some distance from the main drain line requiring a long horizontal run in the machine's drain pipe will also result in a slower flow. Other causes could be: undersized waste pipe, backward wyes or santees, backgraded piping, backed up gray water system.

An obstruction such as a checker piece or poker chip could be lodged within the pipe. Such an obstruction acts as a valve or flap that will pivot out of the way when a snake is pushed through the pipe but pivot closed when water attempts to flow through.

Nowadays a two inch drain pipe is recommended. Some cities require two inches or larger.

Do not seal around where the washing machine hose is hooked onto the drain pipe as this could overload components within the machine.