The BOAT21W is Ronco's heavy-duty answer to the awkward little locker: 8 gallons in a nearly square 17.75 x 15.75 inch footprint that stands just 8.25 inches tall. Squarish tanks like this are easy to brace on all four sides, which is exactly what you want in a sailboat lazarette or under a console seat where the tank will live against whatever bulkheads surround it.
This is the H.D. side of Ronco's marine line - a thicker-walled molding than the standard light-duty RV shells, built for hulls that pound. The polyethylene is FDA-compliant and rated for potable water, so it goes straight into a drinking water system. Ronco has rotomolded these in Tustin, California since 1974, and every tank leaves the plant with fittings spin-welded or thread-installed exactly where you mark them - print the drawing below, plot your inlet, outlet, and vent with the on-page fitting planner, and it arrives ready for hose.
Full, the tank carries about 67 lb of water, and empty it ships at just 8 lb - light enough that one person installs it without help. Compare footprints across the marine range in boat tanks, or see the whole line on the Ronco Plastics hub. OneSource Plastics is an authorized Ronco Plastics dealer.