Shower room sink

A smelling shower cubicle has been the bane of my motor-caravanning life since buying my Symbol. I drove with the cassette out for a while to eliminate the most obvious source (the toilet) but the smell was still there.  Sorry if you are eating or have just finished; but this isn't just a damp dirty mop type of smell, but a putrid, decaying rotten egg stink which becomes apparent from time to time.  Everything suggested on the forum; bio/non-bio washing detergent, bleach, orange drink  etc. has been poured down the shower plug hole and the sink.  For a while the smell would go but would return with a vengeance.  Now planning to drop the waste tank to jet wash it in-case there's a dead rat in there decaying (I  know there isn't but that's what it smells like!)
 Sealant of some kind could be seen around the plug hole so I decided to remove the sink in-case there was a leak.  Well there wasn't but the sealant looked a mess and I'm now debating whether or not to buy a new sink or re-seal the original. How the plug hole got damaged is beyond me unless the pipe was yanked from underneath and broke the plastic surrounding the drain hole. The outside of the shower cubicle has been bleached white by the sun so I'm now debating whether or not to replace that whilst I'm at it. Previous owner had covered it with what looks like very thin carpet. Didn't look too bad but if I can get laminated ply in a similar colour to the rest of the cupboards I might replace the whole panel. Any ideas where I can get the ply-board from in a similar colour, or failing that might recover the original board with Fablon type of stuff if I can fins some wide enough.  Any ideas warmly welcomed.

If you get your build number from the cab glove box and phone Alan Osborne (AS Parts Dept and font of all knowledge) He will give you colour/grain of the ply and its worth asking if they have any (depends how old the van is)

Again dependant on the vans age it could be Fablon (or similar) thats stuck onto ply. Our Windsor is a 2008 model and that full of Fablon which in places looks terrible. Totally different to the proper wood of yester year AS Vans

I am thinking your smell may be due to deposits in the convolutions of the sink waste pipe if you have tried all the usuals for the tank.

Hi Mald we had that problem too especially in hot weather we found the waste tap didn't have a brilliant flow changed it to larger bore and new tap, which we leave open when waste tank empty, it was amazing the gunk that came out and know no whiff at all.
Paul &caz

Thanks both. Will try AS tomorrow for the board - it appears to be laminated ply rather than 'real wood'.  The wood effect is thicker than sticky-backed plastic, the only real wood seems to be the edgings, which could do with a light sand and re-varnish now I come to think of it (another worm just fallen out of the can).
The waste tap is a poor design, my previous MH (Swift Gazelle) had a huge screw off bung which made emptying far easier so might go with your idea of changing the tap to a larger bore!  Oh, well - at least I'm thinking about things other than my 60th tomorrow!! Thanks again. 

'Zappy' does a device to clean the convoluted pipe on the fresh water filler pipe, which I have used very effectively along with the tablets.  This might also work on your convoluted sink drain pipe if you can remove the strainer assembly to get the device down the inside of the pipe:

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One thing I learned from our previous van, which had a tip-up sink with a very small drain hole in the well, was to use liquid soaps rather than 'cake' soap, as the latter tends to accumulate more residues, which encourage bacteria, which is what can lead to the sulphur hydroxide smell.
                                                   

For the wood panel there are a couple of previous threads on the subject to read through..

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I can confirm that the cover applied to the ply-board is a thicker version of Fablon. I have just spent an hour peeling it off!  It was caked in adhesive from the thin carpet used by the previous owner to cover it so it would have looked terrible covered in Fablon-which is what I've decided to do. Thanks for the links Paul - now know that varnishing the real wooden bits is the wrong way to go.
Wash and flush the tank still to do; the Zappy gizmo looks interesting but I would have to disconnect the waste pipe every time I was to use it worth bearing in mind for when I get round to the fresh water side of the van. Thanks all.