I was planning on tying into my washing machine drain stand pipe to add an air gap for my water softener. My original plan was to cut the drain about half way down. Add a sanitary tee, reduce to 1 1/2”, p-trap, 18” stand pipe, topped with a verneco air gap. Then it occurred to me that the washing machine drain already has a p-trap, so I’m assuming that I don’t need an additional one? Do I need to place the sanitary tee any certain way to prevent washing machine water from coming up through the water softener stand pipe?
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