Long, narrow, and shallow - 27" x 10.25" x 6.5" - the Ronco Plastics B287 is shaped for the spaces boats and campers actually have left over: along a gunwale, under a bench seat, beside a wheel well. It holds 7 gallons, ships at 12 lb, and carries about 58 lb when topped up with water, which means it can live on brackets in places a bulkier tank could never be secured.
The B287 is a dual-purpose marine and RV molding, so the same blank becomes a fresh water tank or a gray or black waste holding tank depending on the fittings you order. In fresh service the FDA-grade polyethylene keeps the supply potable; in holding service the thick seamless wall contains odors and chemicals equally well. Ronco installs each spin-weld or threaded fitting to the marks you supply - print the drawing below, sketch where the fill, vent and outlet must sit in your installation, and run it through the on-page fitting planner to be sure nothing collides with a stringer or frame rail.
Ronco Plastics has been molding these odd-space problem solvers in Tustin, California since 1974. Slide over to our boat tanks for the rest of the narrow-profile family, or the RV water tanks if this one is headed for a camper galley. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics B287 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.