Where should a check valve be installed above a submersible sump pump discharge port?

Install a sump pump check valve on the vertical Schedule 40 PVC discharge pipe 2 to 3 inches above the basin lid, positioning it above a 3/16-inch weep hole drilled between the pump discharge port and the valve.

Submersible sump pumps prevent basement flooding during heavy rainstorms by pushing rising groundwater out through a dedicated drainage line. The International Plumbing Code (IPC Section 1113.1) mandates backflow prevention on these lines to stop 2 to 5 gallons of pumped water from draining backward into the basin after each cycle.

If you only do one thing: Mount the check valve above the sump basin lid using rubber compression couplings so you can inspect, clear, or replace the flapper mechanism in under 15 minutes without pulling the pump.

1. Discharge pipe preparation: Thread a 1-1/2-inch male NPT (National Pipe Taper) adapter into the pump discharge port using PTFE thread tape, then solvent-weld a vertical Schedule 40 PVC riser pipe.
2. Weep hole drilling: Drill a 3/16-inch (4.8 mm) air-relief hole into the discharge pipe at a downward 45-degree angle, positioned 2 to 3 inches above the pump outlet and below the check valve.
3. Valve elevation: Mount a full-flow swing check valve vertically at least 12 inches above the pump discharge port, positioning it 2 to 4 inches above the top edge of the basin lid.
4. Union coupling installation: Secure the valve using stainless steel hose clamps on flexible rubber sleeve couplings torqued to 60 inch-pounds to dampen water hammer and permit fast removal.
5. Flow arrow alignment: Verify that the directional flow arrow stamped on the check valve housing points vertically upward, away from the pump and toward the exterior gravity discharge line.

• Watch out for: Missing 3/16-inch relief holes, which trap air bubbles under the flapper, causing the impeller to spin continuously without pumping water until the motor overheats.
• Watch out for: Submerging the valve below the high-water line inside the pit, which leaves mechanical joints underwater and corrodes steel clamps within 12 to 24 months.
• Watch out for: Hard-gluing check valves directly into PVC runs without flexible unions, adding 1 to 2 hours of labor whenever replacing a failed pump or worn valve flapper.

Inspect your discharge pipe clearance above the basin lid and install a rubber-booted swing check valve sized for your 1-1/4-inch or 1-1/2-inch discharge line.