A cassette toilet stores waste in a removable tank at the toilet; a conventional gravity-flush RV toilet sends waste into a holding tank below it. Choose by the plumbing already in the RV, the room for an approved installation and the way you want to access and empty waste. Tank capacity, water supply and fit are model-specific, so compare exact manuals and product dimensions.
The main difference is where waste is stored and how you reach it. A cassette design has a removable tank built into the toilet system; a gravity-flush toilet connects directly above a fixed holding tank. Your existing RV layout and preferred service routine decide which format is practical.
Compare the waste path
Thetford C223-S cassette toilet: The maker lists a 4.7-gallon removable waste tank with wheels and a retractable handle, plus a direct connection to the RV fresh-water tank. Plan for access to remove and handle the tank.
Dometic 300, 310 and 320 gravity-flush toilet: The installation manual places these models directly above a holding tank. Check the existing tank location, mounting space, water connection and service access.
These details come from named product lines. Other cassette and gravity-flush models can differ in capacity, water supply, dimensions and installation instructions.
Choose by the space and service routine
A cassette layout can suit a conversion where a removable holding tank and its access door can be planned into the cabinetry. Before selecting it, check how the tank is removed and where it can be handled and emptied according to its manual and local facilities.
A gravity-flush model is a better fit when the RV layout already has a compatible holding tank directly below the toilet. Dometic’s 300, 310 and 320 series manual is for replacing an existing toilet; it directs owners planning a new or more complicated installation to a qualified service professional. Do not assume one toilet can replace the other without changing or checking the underlying plumbing.
Verify fit, water and waste connections
Measure mounting space, bowl clearance, door swing and access for cleaning or service. Check the exact model’s fresh-water source, waste tank or holding-tank connection, installation manual and winterizing instructions. Keep hose and sanitation equipment separate from drinking-water equipment; the RV sewer hose guide and drinking-water hose guide cover those connections.
Sources
- Thetford C223-S cassette toilet specifications and manual (accessed November 5, 2026)
- Dometic 300, 310 and 320 gravity-flush toilet installation and operation manual (accessed November 5, 2026)
Related: RV sewer hose kit guide, RV drinking-water hose and pressure regulator, RV winterizing checklist, and all van-life gear.
Common questions
Does a cassette toilet need a black tank?
The Thetford C223-S example has its own removable 4.7-gallon waste tank and connects to the RV fresh-water tank. Other models can have different plumbing, so check the product manual.
How is a cassette toilet different from a gravity-flush RV toilet?
The cassette stores waste in a removable tank, while Dometic's 300, 310 and 320 gravity-flush series are installed directly above a holding tank. These are model examples, not universal layouts.
Can I replace a black-tank toilet with a cassette toilet?
Only if the new toilet fits its mounting space, freshwater supply and service access. Dometic advises consulting a qualified service professional for a new or complicated toilet installation; follow the exact cassette model instructions too.
What should I measure before choosing an RV toilet?
Check the opening and mounting dimensions, bowl and door clearances, water connection and access needed for maintenance or a removable tank. Use the toilet maker's installation drawing for the exact model.