I bought a house with a slab foundation that came with an efficiency under the counter washing machine. This machine came with a drain line has an attachment on it that connected under the counter to the drain pipe. I replaced that attachment by extending the drain line and created the stack line 39" off the frond. I tested the drain and failed because the drain is filling up and water comes out over the top of the stack. I think my mistake was using the same 1 1/2 " piping that was originally there. They had reduced to get that. I think my issue is not using 2". Any thoughts?