I assume you mean the 'Pink flush additive' fragrant smelling fluid which helps to keep bowl and seals clean and the smells down, I often wondered about that not having a motor home and it being fed from the main tank by electric valve. simple answer no looking up the design.
however don't take my word for it 'ask thetford' and while your on site download their free repair pdf's for your toilet. see below thetford access.
For UK & Europe www.thetford-europe.com
Australia www.thetford.com.au (even get request from australian campers)
australia site has stockist list.
home page select english {if in Australia forget this selection it doesn't come up)
select Customer service (top line)
select Products top line (top line)
select Bulit 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 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.
as you go through watch for 'ask thetford' on left listings
you may not find what you want and you can send them a message.
for safety reasons which i agree with thetford do not offer repair advice for fridges. refer to service centre
Bob
August 2010