What size ABS pipe is required for a washing machine drain, which will also serve as a drain for an adjacent washtub?

Washer stand pipe = 1 1/2"
Two inches would be better.

In my area, Code requires 2" drain for washing machine and 1 1/2" drain for service sink ( wash tub ). They can be combined into one drain which will have to be 2" at the point of connection.

Besides the drain, Code calls for 2" P-trap and 2" stand pipe (30" tall ) for washing machine plumbing. With today's high output washers, smaller diameter pipes will most-likely be inadequate and will overflow.

Hope that helps

Milo

They don't allow ABS in new construction in GA anymore. Do you have ABS piping?