Thetford toilets 2
Type C 200 toilets have a water filter located high up under the bowl near the seat moulding. After some time this can become choked and effect the flushing action of the toilet. To clean this filter, first remove the cassette, and then unscrew the clamps holding the bowl to the base unit. Then carefully turn the bowl upside down to access the filter which is held in place with two hose clips. After cleaning the reverse procedure is used to reinstall the bowl.
Info from Bill Mulliner.