This Old House plumbing and heating expert Richard Trethewey shows how to install an emergency backup sump pump
1. Attach two 3-foot-long 2x3 cleats to the wall above the primary sump pump; fasten the cleats with 3-inch screws.
2. Screw the backup sump pump to the 2x3 cleats using the mounting hardware provided. Be sure to set the float on the backup pump slightly above the height of the primary pump.
3. Next, cut into a nearby cold-water line and run ¾-inch-diameter copper pipe down to the control valve on the backup sump pump. Solder each connection with a propane torch and lead-free solder.
4. Unplug the primary sump pump. Then, drain water from the existing discharge pipe by using a slotted screwdriver to loosen the band clamp on the check valve.
5. Cut into the into existing discharge pipe leading from the primary sump pump, and run a new 1½-inch-diameter PVC discharge pipe from the backup pump.
6. Install a new check valve onto the backup pump, then use PVC pipe primer and cement to clean and solvent-weld together the plastic pipe and fittings.
7. Disassemble the backflow preventer, then open the water valve to flush any solder or flux into a bucket.
8. Fill the sump pit with water, plug in the primary pump and wait for it to turn on.
9. Unplug the primary pump and raise the float on the backup pump by hand to simulate water rising in the sump pit. When the float reaches the appropriate level, the backup pump will kick on and drain the water from pit.