the thetford wc

I lifted out the wc roll cylinder and under the plastic container there is the flush water but no top on it, is this right? 

Bit late responding to this, sorry

But, yes, once you take the cylinder the loo roll sits in, that's what you see. There is an O ring on the roll container that stops it leaking...these go hard and split, so you might see a bit of leakage if that's the case. They're about £4 to buy.

This is an Aussie site, but was the first link I found with the right image.

https://www.caravanparts.com.au/diagrams/toilet/thetford/c2-cassette-toilet/

Part 25 is the O ring, 24 is the tube the loo roll sits in.