Poo Math › Guides › RV holding tank sizes explained (fresh, gray, black)
RV holding tank sizes explained: fresh, gray, and black
An RV carries three separate tanks. The fresh tank holds clean water for showering, drinking, and washing. The gray tank collects used water from the shower and sinks. The black tank holds toilet waste. Knowing the size of each is the key to planning a self-contained trip to Burning Man, where there are no hookups.
Most rentals and mid-size rigs hold roughly 25 to 45 gallons of gray and black each, while fresh tanks range from about 20 gallons on a small camper to 90-plus on a large motorhome. Gray almost always fills first because showers and dishes generate the most water; black fills more slowly. When a tank is full you are done until it is pumped out, so the smallest relevant tank sets your service schedule.
Poo Math includes presets for common rental and trailer models — Cruise America, El Monte, Airstream, fifth wheels, and more — so you can start from real capacities instead of guessing. Pick your rig and it estimates pump-outs and water refills for your crew.
Plan your trip in the calculator →