ABS reducing coupling for joining two different-size ABS DWV pipes in one solvent-welded step — the fitting that steps a 3-inch stack down to a 2-inch branch, or a 2-inch line into 1½-inch, without stacking adapters. Both ends are hub sockets sized for Schedule 40 IPS ABS, so each pipe seats to full depth before the cement sets. The coupling meets ASTM D2661 and CSA B181.1 and carries cUPC certification, the listing an inspector checks on a residential or light-commercial drain, waste, and vent rough-in across the GTA. ABS keeps the fitting light on overhead work and rigid once the run is strapped. Stocked in the three reductions that cover most kitchen, bath, and stack transitions — 2×1½", 3×1½", and 3×2" — a low-cost part you reach for whenever pipe sizes change mid-run.