My washer drains into the common 2-inch PVC standpipe that's about 36
inches tall. It bottoms out in a P-trap, then runs about 18 inches
horizontally before it enters the main waste stack.
The laundry sink (beside the washer) also has the standard P-trap, but
the drain pipe runs three feet horizontally and joins with a waste-T to
the washer standpipe about 6 inches above the standpipe P-trap.
Is the laundry sink double-trapped? If so, given that the washer
standpipe is its own vent, is this a problem?
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