minimum size drain pipe for washing machine
3. Compare the fixture to the Minimum Sizes of Drainage Pipe by Fixture table. For instance, the minimum pipe diameter for a washing machine drain is pipe with a 1 1/2 inch diameter.When combined with a laundry tub, the drain pipe must be a minimum of 2 inches in diameter.. Compare the fixture to the Minimum Sizes of Drainage Pipe by Fixture table. For instance, the minimum pipe diameter for a washing machine drain is pipe with a 1 1/2 inch diameter.