The Ronco Plastics B281 packs 21 gallons into a near-cube - 19.88" x 16.88" x 16.38" - which is the most efficient way to get real capacity through a small locker opening. Cubes waste the least wall area per gallon, so this molding runs heavy on volume and light on footprint: 22 lb empty, roughly 175 lb with a full load of water aboard. That density is worth respecting when you pick the shelf it lives on.
Like the rest of Ronco's marine B-series, this is a dual-purpose molding: order it with fresh water fittings and the FDA-grade polyethylene serves as a potable supply tank, or order it as a gray or black waste holding tank and the same wall thickness handles the uglier job. The role is decided entirely by the fittings, which Ronco spin-welds or threads in at the exact spots you mark. Print the drawing below and work out your port locations with the on-page fitting planner - it is the one step that makes installation day boring, in the good way.
Ronco Plastics has molded these tanks in Tustin, California since 1974, and the B-series remains the refitter's standby because the geometry catalog is so deep. Compare footprints across our boat tanks, or look at RV holding tanks if this one is destined for a coach rather than a hull. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics B281 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.
