Twenty gallons is the point where a boat stops rationing water on a weekend. The B165 gets you there in a single marine molding that Ronco runs as a dual-role shell: specified fresh, it is potable-grade FDA-compliant polyethylene; specified as a holding tank, the same geometry serves gray or black waste. The role is fixed by the fittings you order, not by the mold.
Budget the weight before you pick the spot: 20 gallons of water runs about 167 lb, so the tank belongs on structure - stringers or a shelf tabbed to the hull - not on unsupported liner. Empty, the blank is a 25 lb lift, easy to trial-fit alone.
Ronco has molded in Tustin, California since 1974, and every B165 leaves with its fittings spin-welded or thread-installed to your marks. Print the drawing below, mark suction, fill, and vent where your plumbing wants them, and set it all up in the on-page fitting planner. If the installation is a trailer rather than a transom, the 20-gallon RV39W covers the same capacity in the light-duty RV line.
The full range is under boat tanks and the Ronco Plastics hub. OneSource Plastics is an authorized Ronco Plastics dealer.
