Twenty-one gallons is a deliberately odd number, and odd numbers are how you know a tank was molded for a real space in a real hull rather than a round-number spec sheet. The B110 fills a marine recess that 20-gallon tanks rattle in and 25-gallon tanks will not enter. If you have measured your locker and come up between the standard sizes, this may be the molding that was drawn for it.
It is a fresh water tank in FDA-compliant potable polyethylene - seamless, no liner, no joints - with a 29 lb empty weight that signals a thicker wall than the capacity demands. Full, it holds about 175 lb of water at 8.34 lb per gallon. The same blank can be ordered as a waste holding tank instead; fittings, not molds, define the role.
Ronco installs those fittings per order in Tustin, California, where the shop has rotomolded since 1974: print the drawing below, mark your locations for spin-weld or threaded fittings, or drop them on the on-page fitting planner. Every neighboring size and shape is in boat tanks, with the full catalog on the Ronco Plastics hub. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics B110 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.
