A 25-gallon dual-role tank is the most useful single molding a mid-size boat can carry, and the B115 is Ronco's: order it with fresh-water fittings and it is a potable supply tank in FDA-compliant polyethylene; order waste fittings and it is a full-size holding tank for a cruising head. Same blank, opposite jobs, chosen at order time - it ships plumbed for neither until you decide.
The numbers are friendly. Empty it is 32 lb, manageable solo through most companionways; full it holds about 208 lb of water at 8.34 lb per gallon. Twenty-five gallons of fresh supports a genuine weekend for a small crew, and twenty-five gallons of holding capacity buys the kind of pump-out schedule that keeps a boat civilized.
Fittings are installed per order at the Tustin, California plant, where Ronco has rotomolded since 1974: print the drawing below, mark your fitting locations, or set them on the on-page fitting planner, and the tank arrives spin-welded or threaded to your plan. Compare the marine shapes in boat tanks, the land-going equivalents in RV holding tanks, and the whole line on the Ronco Plastics hub. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics B115 dimensional drawing - print it to plan your install and mark exactly where you want fittings located; Ronco installs spin-weld or threaded fittings to your marked spec.
