Came across this on one of the forums and it sounds
like an idea worth try. When we returned from extensive touring of South Australia
our Thetford cassette had a heavy lining of sediment - a nightmare to remove mechanically.
"Every 6 to 8 weeks empty a packet of citric acid (often available
in the baking section of the supermarket) into the empty cassette, 3/4 fill the
cassette with water. Over a period of 5 to 6 hours turn the cassette over a couple
of times. After this empty the cassette and rinse out. This removes all the scale
build up and leaves the interior of the cassette very clean. I tried it out yesterday
and as suggested, it did leave the cassette toilet very clean and no odour in
the cassette at all."
On the same forum this was a follow up post.
"As well as using citric acid to clean out the Thetford toilet, we also
use citric acid every couple of months in the following ways:
In our Lemair
washing machine, 2 or 3 tablespoons in the bottom then fill with water and complete
one cycle of the machine, clears all the soapy gunk out of the waste pipes.
Down the waste pipe of the shower, hand basin and kitchen sink - 2 or 3 tablespoons
drizzled into the waste pipe, followed by a small amount of water - just enough
to form a paste which will trickle down the waste hose, leave for a while, then
slowly pour some boiling water down the waste drains, followed by a good flow
of cold water. You will be amazed at the gunk that comes out of the pipes. "
have not tried the Thetford idea yet so we cannot say if it will for instance
have any effect on Bio Magic. We can't see it doing anything nasty to the Thetford