Ronco Plastics 12H - 18 Gallon Plastic RV Holding Tank (22.0" x 23.0" x 12.5")

The 12H goes deep instead of wide: 18 gallons in a 22 x 23 x 12.5 inch cube, the deepest draw in its capacity class. A tank like this occupies a compact square of floor - barely two feet on a side - and pays for it in height, which makes it the natural pick for bays under dinette seats and in vertical chases where footprint is scarce but headroom is not.

Depth has a plumbing advantage waste tanks care about: a 12.5-inch liquid column drains harder and cleaner through the dump valve than the shallow puddle in a low-profile tank, carrying solids out with it. The blank ships at 18 lb; full, it holds about 150 lb of gray or black water concentrated on that small base, so the floor under it must be structural.

Two cube-family relatives bracket it: the 56H with 21 gallons at 22 x 22 x 12 inches and an end dump, and the 10H at 22 gallons and 34 x 22 x 12 inches when you can spare more length. The rest of the shapes are in the RV holding tanks category.

Strictly waste service - never fresh. Ronco rotomolds the 12H in Tustin, California, as since 1974, and installs your fittings to order: print the drawing below, mark your fitting locations, choose spin-weld or threaded. OneSource Plastics is an authorized Ronco Plastics dealer.

Technical drawing: download the Ronco Plastics 12H 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.