Product details:

This Icon RV Waste Holding Tank with Bottom Drain has reinforcements built right in so you can mount a toilet directly on top of it. The holding tank comes with a 3 threaded fitting, a 1.5 slip fitting, and a flange fitting that has a 3 ID and 7 OD. No additional fittings are needed. All seams are solvent welded and have a 1.25 mounting flange.