Most RV toilets are gravity flush. A foot pedal opens a valve in the bottom of the bowl, a little water rinses it, and the waste drops straight down into the black tank underneath. The other types grind and pump the waste, or hold it in a removable cassette.
RV Toilets Explained: Gravity Flush, Macerating, Cassette and Portable
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At a glance
- Most common type: gravity flush, where a pedal opens a valve and the waste drops straight into the black tank below.
- Water in the bowl: the makers want some left in after every flush, because it seals tank odor out of the bathroom.
- Your model: the maker's model label is on the toilet base or the back of it, and it decides which seal and water valve fit.
On this page (8)
How does an RV toilet work?
One pedal does two jobs. Press it part way and water runs into the bowl while the valve stays shut; press it all the way down and the valve opens, so the bowl empties into the tank below. Dometic and Thetford both describe this two-stage pedal, and Jayco calls the Dometic-style valve a ball valve.
The rinse water comes from the fresh tank by way of the water pump, or from the city water inlet when you are hooked up. There is no household-style trap: Dometic's gravity-flush manual says these toilets discharge directly into a holding tank and that horizontal pipe runs should be avoided. Thetford puts RV flush water at about 1 quart, against 1.6 gallons for a home toilet, so flushing longer than needed fills the tank faster.
Tip: Use the half-pedal before you use the toilet, not just after. Dometic recommends adding water to the bowl before flushing solids and paper, which keeps both from sticking on the way down.
The types, and which one is in your RV
A foot pedal over the black tank means gravity flush, which covers most travel trailers, fifth wheels and motorhomes. A wall controller or push-button flush usually means a macerating toilet, such as Thetford's Tecma Silence Plus 2G or Dometic's 8700 MasterFlush. A door on the outside wall behind the bathroom means a cassette, and dry units with no water line are composting toilets in an RV.
| Type | How it flushes | Where the waste goes |
|---|---|---|
| Gravity flush | Foot pedal opens a valve in the bowl | Straight down into the black tank |
| Macerating | Button runs a pump that grinds the waste | Pumped along a line to a holding tank |
| Cassette | Pedal or button, blade valve under the bowl | Removable tank pulled out from outside |
| Portable | Bellows, piston pump or electric button | Lower tank that detaches and is carried |
| Composting | No flush water | Held in the unit, not a black tank |
Descriptions as Dometic and Thetford state them in their owner's manuals and support pages.
A macerating toilet can sit away from the tank. Dometic rates the 8700 Series MasterFlush pump to move waste up to 98 ft, and Thetford says the Tecma Silence Plus 2G moves it up to 120 feet. The 8700 needs a 20 amp, 12 V DC circuit breaker, and Dometic recommends a qualified RV technician or electrician for the install.
Is it supposed to hold water in the bowl?
Yes. Dometic says the water left after a flush makes an airtight seal that stops holding tank odors from entering the living space, and Jayco adds that it lubricates the ball valve seal.
How deep depends on the document: Dometic asks for 1 in., while Jayco's 2027 towable manual says at least 2 inches and its Class C manual four to six. Follow your own toilet's manual and never leave the bowl dry. Cassette toilets are the exception: Thetford says not to leave water in the bowl when the toilet is not in use.
Where to find your toilet's model label
Seals, water valves and replacements are model-specific, so find the label first. Dometic puts it on the base under the water valve on the 300, 310 and 320 series, and on the back of the base on the 400 series. Thetford's data tag is usually on the back of the toilet, sometimes on the base, and removing it can void the warranty.
A bowl that will not hold water, or a pedal that will not flush, is a repair question: see RV toilet problems.
Tip: No tag left? Thetford identifies a toilet from three things you can see: whether it is a hand, foot or wall panel flush, how many pedals or buttons it has, and whether the bowl is porcelain or plastic. Note all three before replacing the toilet or ordering a kit.
What the Dometic and Thetford model numbers mean
Within each line the number mainly tells you the bowl material and the seat, and each model comes in a standard height and a low profile for short bathrooms.
| Model | Bowl | Seat height, high / low |
|---|---|---|
| Dometic 300 / 301 | Polypropylene | 18.25 in. / 14 in. |
| Dometic 310 / 311 | Vitreous ceramic | 18 in. / 13.75 in. |
| Dometic 320 / 321 | Vitreous ceramic, wood seat | 18.25 in. / 13.5 in. |
| Thetford Aqua-Magic VI | Polypropylene | 17.8 in. / 13.9 in. |
| Thetford Residence | Polypropylene | 18 in. / 12.5 in. |
| Thetford Aqua-Magic Style II | Ceramic bowl, polypropylene base | 18 in. / 12.5 in. |
| Thetford Style Plus | Ceramic bowl, polypropylene base | 17.5 in. / 12.9 in. |
Dometic figures from its 300, 310 and 320 series manual; Thetford figures from its RV toilet support page; the same owner's manual also covers the Bravura. The Aqua-Magic V is discontinued but still fitted in many older RVs, and Thetford keeps its manual and service kits online.
Porcelain or plastic bowls
Plastic means polypropylene, which is light; porcelain means vitreous ceramic, which is heavier and wipes clean like the toilet at home. Thetford's Style line sets a ceramic bowl on a polypropylene base.
Clean either one gently. Thetford warns that household bowl cleaner acids dull and pit an RV bowl, that bleach damages the seals, and that acids or concentrated cleaners can void the warranty; Dometic allows rubbing alcohol on stains in its polypropylene 300 and 301 bowls only. Use a non-abrasive RV bowl cleaner, a soft brush and septic-safe RV toilet paper.
Cassette and portable toilets
Both store the waste in a tank you carry to a dump point, so they suit vans and small trailers with no black tank.
- Cassette: the toilet is fixed and the tank slides out through a door in the side wall. Thetford's US C223-S has a 4.7 gal tank on wheels; Dometic's CT 4000 uses a 19 liter (about 5 gal) cassette.
- Portable: the whole unit lifts out, and the lower waste tank separates from the upper fresh water tank. Dometic's 970 series comes in 2.6 gal and 5.0 gal sizes.
- Emptying either one: at a toilet or legal dump point, point the spout down and hold the vent button in while it drains so it does not splash back, then rinse with clean water.
Tip: Thetford calls the blade valve seal in a cassette toilet a wear part. Keep household cleaners, bleach, solvents, Vaseline and vegetable oil away from it, and replace it when it wears.
Common questions
Is an RV toilet supposed to hold water in the bowl?
Water may keep trickling into a ceramic Dometic 310, 311, 320 or 321 for up to 20 minutes after flushing because of the integrated rim, and that is normal. If it is still trickling after 30 minutes, Dometic says to replace the water valve.
What is the difference between the Dometic 310 and 320?
Both have a vitreous ceramic bowl, so they flush the same. The 320 has an enameled wood seat and a larger minimum clearance, so measure the space before swapping one for the other.
Which is better in an RV, a porcelain or a plastic toilet?
Neither maker ranks one above the other. Choose on weight and feel, then check the space: Dometic lists a different minimum clearance for each model, from 8.5 in. on the 300 to 11 in. on the 320.
How often do you empty a cassette toilet?
By the tank level, not the calendar. Thetford's C-200 lights a warning lamp once the tank holds more than 15 liters (about 4 gal), which leaves roughly five more uses. Thetford suggests emptying a Porta Potti 100 series every 4 to 5 days.