Seals on cassette loo

Not really.

No,  but  you  must  be  prepared  to  insert  your  hands  inside  the  cassette  !

{  I  was  going  to  say  why  do  you  let  the  seals use  your  Loo,  but  I  really  shouldn't    !  ) 

YouTube it step by step info 

Disposable gloves can be useful.

As already mentioned there are You Tube videos.  You can also download instructions from the Thetford website and get the correct part number for your model of loo – this is important as there are several different types.  And finally there are instructions in the pack!

Moderator Edit:

Your post has been amended to reduce the size of the text.

I'm no diy'er but changed mine a few weeks ago.  Fairly straight forward but gloves essential!!!!  Get some Silicone Spray as well to lubricate it all. 

on most cassettes the centre section (containing the 'hole'and blade mechanism) can be extracted from the cassette to make maintenance (and cleaning) much easier..

Yes, but they vary.  Repalced mine a couple of weeks ago and it was as you describe BB.  First had to take out the 8 screws then turn the casstte grey sliding cover (at last a use for it!)  the wrong way round and use it as a lever to twist off the sliding mechanism to get access to the seal.  Once you have removed the mechanism turn it over and remove the screw which holds the sliding cover, and remove the slide, to get access to the seal.  When refitting spray all wiith silicon spray to aid fitting and operation.  The hardest part was twisting off the sliding mechanism as I was worried that I might break the cover.  I now have a very clean cassette with a good seal!  As I said above, this is all within the cabilities of most of us.  On some models you just remove the 8 screws (4 may be under the 2 covers) and then lift out the seal and replace.

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"Seals on cassette loo"

If you're caught short and desperate, you could try tempting it off with a mackerel.