The best way to tackle this is to print off a copy of the PDF for spare parts for your toilet. The exploded diagram is helpful in determining what parts can be removed to get at the more remote bits.
Here's how to get the diagram:
Log onto:
www.thetford-europe.com
Home page. Select English
Select customer service (top line)
Select products from top line
Select built in or portable which ever applies.
Select user information from list on right.
Select repair instructions from list on right
Select built in or portable which ever applies.
Select your toilet series model number from right list.
You will now be in the pdf listings for your range of toilets just select those that apply to your toilet and down load them they're free.
CC Member 18017873, May 2012