Holding Tanks

Sizing a replacement RV holding tank

Holding tanks are one of the few RV parts where fit is unforgiving — the tank has to drop into a specific space between frame rails and clear the drain outlet, so the dimensions matter as much as the gallon rating. Molded ABS tanks like the Icon and Valterra units here are the standard replacement, and most waste tanks come with the level sensor bungs already installed so your monitor panel keeps working.

• Measure before gallons. Match length, width, and height to the space you're filling. A 20-gallon Icon tank comes in a 32" x 12" x 12" shape and a taller 39" x 16" x 16" shape at the same capacity, so the footprint decides which one drops in.
• Drain location. Tanks come center-end-drain or side-drain (the Icon HT175B-ED is center end drain, the HT292SD is side drain). The drain has to line up with your existing valve and plumbing run, so confirm which side yours exits.
• Level sensors. Most waste tanks here ship with four pre-installed sensors that read empty, one-third, two-thirds, and full. If your old tank had a working monitor, get a tank with matching sensor bungs so you can wire it back up.
• Fresh vs. waste. Fresh water tanks (the 12- and 20-gallon Icons, the Valterra R8030) and black or gray waste tanks look similar but aren't interchangeable in placement or fittings. Buy the type for the job.

When you drop a new tank in, plan on new tank fittings and a fresh gate valve at the outlet — reusing brittle old parts on a new tank tends to leak again within a season. Fresh-water tank swaps tie into the fresh water system on the supply side.