Forty gallons from a 23.5 x 23 inch patch of floor - the B221 is what happens when a tank gives up on sprawl and builds upward instead. At 23.5 x 23 x 18 inches it is nearly a cube, and cubes are the most volume-efficient shape a rectangular locker can hold. If your available space is a deep bench seat, a corner of a cargo bay, or a locker that low-profile tanks would squander, this is the geometry that uses all of it.
It is a dual-role molding for marine and RV systems: fresh water or waste holding, decided purely by the fittings you order on the blank shell - never pre-plumbed. Fresh service rides on FDA-compliant, potable-rated polyethylene; waste service uses the same seamless rotomolded wall. At 33 lb empty it moves easily; at about 334 lb full (8.34 lb per gallon) it concentrates real weight on a small footprint, so put genuine structure under those 23.5 x 23 inches rather than trusting floor sheathing.
Print the drawing below and mark your penetrations for the role you choose - fill, vent, pickup for water; inlet, vent, dump for holding - or place them on the on-page fitting planner. Ronco spin-welds or thread-installs each fitting to your marks in Tustin, California, the way the shop has built tanks since 1974.
Compare the cube against the flats in the boat tank category and RV water tanks, or browse the entire line on the Ronco Plastics hub. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics B221 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.
