Eight gallons in a squarish 17.75 x 15.75 x 8.25 inch tray - the 21W is sized for the systems people forget to plan: the outdoor shower feed, the dedicated dish-rinse supply, the gray catch under a small galley, the fresh tank in a truck camper where the "tank compartment" is really just a gap. Its name on Ronco's sheet says it plainly: fresh or grey, one molding.
That is the Water / Waste Holding Tank series promise. With potable fittings it is a fresh tank in FDA-compliant polyethylene; with drain fittings it quietly swallows sink water instead. The shell itself does not care - your fitting order is what commits it.
At 8 lb empty it installs one-handed; full it holds about 67 lb of water (8.34 lb per gallon), light enough that even cabinet-floor mounting is realistic if the floor is screwed to structure. If eight gallons is the right idea but the wrong shape, the RV water tanks category has this capacity in longer, thinner profiles, and RV holding tanks covers the waste side from 7 gallons up.
Rotomolded in Tustin, California since 1974. Fittings are installed per order - spin-weld or threaded, exactly where you put them: print the drawing below and mark it, or use the click-to-place fitting planner. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics 21W 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.
