flush twist is very very hard to turn thetford casette ?

www.thetford-europe.com has good repair download and at start you can 'Ask thetford' put this to them see what they come back with. Follow instructions for site access.
Inst:

UK www.thetford-europe.com
Australia www.thetford.com.au
Australia site has stockist list.
FOR UK USERS.
HOME PAGE SELECT ENGLISH {if in Australian forget this selection
NEXT PAGE SELECT CUSTOMER SERVICE (tope line)
NEXT PAGE SELECT USER INFORMATION (left of pic)
NEXT PAGE SELECT REPAIR INSTRUCTIONS (left of pic)
NEXT PAGE SELECT BUILT IN TOILETS [top right of pic]
NEXT PAGE SELECT C2, C3., C4 (or relevant) or select your model
NEXT PAGE PDF Files YOU ARE NOW IN PDF FILE LIST.
It would be interesting what they say about the flush/blade knob post it

bob
April 2009