You are obviouly aware the c3 uses electric non return valve in place of a pump. I assume you are concerned about contamination or just want to change it.
If you go to www.thetford-europe.com or those in Australia www.thetford.com.au (world forum) then you can download instalation instructions and other stuff you want for free. Having any trouble just look for 'Ask Thetford' in the menu lists and send online message. You may already know the following but here goes anyway.
The C2 has electric pump
The C3 has electric non return valve and is hygenic or they would not be allowed to fit/manufacture this system.
The C4 (mine in my Lunar Solar caravan) has manual pump basically all the same units.
The only difference is the water fill tube on C2 and C4 you have to ensure there is room to pull this out which if not enough room on the C2 you can over come this by filling the flush tank by removing the toilet roll holder in the tank it just lifts out smear with vaseline before replacing to make it easier to remove.
If in doubt don't be put off ask the experts at Thetford .
Bob
April 2012
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