Spears 854-030 3” PVC Van Stone Flange SOC CL150. Available at commercial plumbing supply vendors.

3” PVC Locking Waste fittings by Valterra. Available at RV vendors.

Not shown:

Valterra Master Blaster Tank Wand A01-0184VP. This 27” wand hooks up to a charged garden hose on one end and has a 90° pressure nozzle to lower into the tank.

L