Thetford c2 will flush, but will not open, WHY?

I had same problem and put a belt on the knob to assit with opening it worked from there on even though I oiled the blade it still stuck so each time didn't fully close it until time for emptying then it has to be closed fully but strange seemed to work easy when out. I'm checking with thetford see if they have solution if I get reply I'll post what they say.

Nobby
April 2009