I am trying to add a utility sink in my laundry room. Right now, the washer drains into a cast iron standpipe coming out of a concrete slab floor with the P trap below the concrete slab floor. Directly next to the standpipe is a cast iron vent pipe that connects to the system below the floor and vents through the roof. I would like to cut the standpipe down and replace with PVC. Then I'd like to tie the utility sink into the new pvc standpipe below the point where the washer would drain into without putting a p trap directly below the sink. Thus the standpipe p trap would serve both the washer and the sink. Is this possible/allowed?
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