Remove the cassette and undo the stainless steel screws around the slide opening (keep the blade closed until you have undone and removed the screws so none will drop in the tank)
Remove the lip seal cover and open the blade. The lip seal will lift out.
Place new seal in position and reassemble without closing the blade. Apply a little Vaseline to the underside of the lipseal and gently close and open the blade a few times to work it in.
There is an exploded view of all the parts making up these cassettes on the Thetford web site.
Finally fill the cassette with fresh water and stand it on end to make sure you have a non leaking seal
Geoff inside Wales, July 2010
