The 12 volt flush pump on our 402C went short circuit and blew the fuse when it failed completely after a very short time.
A replacement pump from the Thetford master agents was $135 - and I now considered these to be of poor quality.
I bought an equivalent size good quality submersible pump for just $35 from :-
http://www.trademe.co.nz/motors/caravan ... 093275.htm (recommended)
These pumps are not all that hard to replace.
Full instructions along with plenty of photos at :-
http://www.thetford-europe.com/en/servi ... tions.aspx
Click on "Repair instructions for all Thetford Sanitation products" to download the 10 Mb .pdf file.
See Pages 125 - 127..