how can I fix my c200 cw?

Don't know but you could contact www.thetford.com and ask what might the prob be. You can also see the PARTS list [better drawings than the manual as it lists and names all parts] un-fortunately doesn't show the manual pump/flush.
Click parts on home page select permanent toilets from the dropdown menu. Select your model [middle picture 3rd down] up comes the exploded veiw of the toilet and below is the parts list name and numbered.
Worth saving to file for reference and better than manual picture.

bob
September 2008