What makes the C403-L different
The C403-L is a permanently installed cassette toilet. Its bowl stays in the bathroom while a 19.3 L waste cassette is removed through an exterior service door for emptying.
Unlike the C402-X, the C403-L does not have its own 15 L flush-water tank. It takes flush water from the camper's central fresh-water system.
Central-water connection changes the plumbing
The toilet's flush supply depends on the main water system. That means a problem with pump pressure, central water supply or isolation can also affect toilet flushing.
MHS explanation.Do not follow a C402 winterizing diagram and assume the C403 has a separate tank to drain. Identify the exact version first.
Electric flush
The flush is electrically operated. Older Thetford installation material describes C403 flushing through a central electric valve/relay arrangement using the vehicle's water supply.
Before service, isolate the appropriate electrical supply. A failed flush does not automatically mean the waste cassette is faulty; water supply and electrical control are separate parts of the system.
Waste capacity and level indication
The removable waste tank is 19.3 L and has three level indications. The tank has wheels and a handle to make transport to a disposal point easier.
Capacity does not translate into a fixed number of days. Usage depends on occupants, flush behaviour and whether the toilet is the only sanitation option.
Size and seating height
The technical overview lists 512 × 670 × 400 mm and a seating height of 473 mm. Net toilet weight is 8.1 kg in the referenced technical table.
These measurements do not include all service clearance. The cassette must slide fully out through the service door and the installation must remain watertight where the toilet meets a wet-bath layout.
Left- and right-hand installations
The C400 range includes left- and right-hand arrangements depending on which side the waste cassette is removed. Regional/current part numbers can also differ.
MHS explanation.This card therefore records the C403-L model's common technical characteristics, not one universal part number. The actual data badge should be used for replacement parts.
Sanitation and servicing
The waste cassette is designed for hygienic removal and emptying at appropriate facilities. Keep sanitation accessories separate from drinking-water equipment.
After emptying, inspect the seal and moving parts as instructed. Do not use incompatible cleaning chemicals merely because they are strong household cleaners.
Winterizing
The central fresh-water system and toilet flush connection must be drained as part of the camper's winter preparation. The waste cassette should also be emptied and maintained according to the manual.
Water can remain in valves or low points even when the main tank looks empty. Follow the installed camper's drainage sequence.
What to check when buying or servicing
Locate the data badge and confirm C403-L. Check the exterior service door, cassette removal direction, electric flush, central-water connection and level display.
If replacement parts are needed, use the serial/model information rather than choosing by appearance. The C402 and C403 share a body style but not every water-system component.
Key takeaway
C403-L combines a fixed toilet with a removable 19.3 L cassette and uses the camper's central water system for electric flushing. Its main practical differences from C402-X are the absence of a separate flush tank and its dependence on the RV water supply.
Sources
A practical service-door test
Before a trip, remove the empty cassette and put it back while the camper is loaded as it normally would be. Check that the exterior door can open fully, the handle has room to extend and the cassette clears nearby jacks, steps or stored equipment. These practical clearances are part of a usable installation even though they are not included in the toilet body dimensions.
Common C403-L specifications; regional/production-year part numbers may differ. Do not transfer the C402-X integrated flush-tank arrangement.