Thetford c4 sliding cover, what does it do

To be honest, I think it's there just to make the thing look a bit neater. It does seem a bit over the top, because they also have to fit a mechanism for opening it, as well as the flap, when you use the toilet. The cover probably also provides more of an
air tight seal to prevent odours entering the van (I doubt that the flap is a very good seal).

However, if you do replace it, I would suggest that you also replace the rubber seal on the cassette. My cover became very loose and was also in danger of falling down the drain every tme I emptied the cassette and replacing the rubber seal solved the problem
as it increases the friction on the sliding cover.

The rubber seals are available on Ebay etc and are easy to fit.

I make it a rule to remove the sliding cover and filler cap before introducing the cassette anywhere near the emptying point, having lost both items down the drain in the past. Some service points have a shelf or similar provided for this, but most don't,
and I confess to not being entirely happy placing them nearby on the ground, for hygeine reasons.

+1

 ..... and I confess to not being entirely happy placing them nearby on the ground, for hygeine reasons.

Why? Just in case someone decided to have a pinic next to the elsan waste point? I put the cap on the floor as I really don't want to go fishing for it ...... 

No!!!  because somebodies dog usually comes along and wants to b*##%r off with it

Heaven knows!   what someone else’s dog has had in its mouth  
.