Buy the 7W for one job and it will do either. This 35-gallon molding is Ronco's dual-role blank: plumbed with fresh-water fittings it serves as a supply tank, plumbed for drainage it becomes a gray or black holding tank. The mold does not care - the fittings you order decide the job, and nothing is plumbed until you decide. At 30 x 22 x 14 inches it is a wide, squarish footprint that suits open bays in both RVs and boats.
Used fresh, the material story matters: FDA-compliant polyethylene, safe for potable water. Used as a holding tank, the same wall shrugs off waste chemistry. Either way you are hanging real load when it is full - 35 gallons of water runs about 292 lb at 8.34 lb per gallon - against an empty weight of just 19 lb, so build the cradle for the full number, not the empty one.
Fittings are installed per order in Tustin, California, where Ronco has rotomolded tanks since 1974: print the drawing below, mark your spin-weld or threaded fitting locations, or drop them on the on-page planner, and the tank arrives drilled to your plumbing plan. Comparable shapes for each role live in RV water tanks, RV holding tanks, and boat tanks; the whole line is on the Ronco Plastics hub. OneSource Plastics is an authorized Ronco Plastics dealer.
Technical drawing: download the Ronco Plastics 7W 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.
