recently had problem with toilet pump not working,fuse not blown so removed cover on top tank inside of van. Removed 4 screws & internal cover bracket removed hose from clip and lifted out electric pump.surpised by amount of black gunge around pump & inside of top tank. Checked inlet on bottom of pump & found impeller sticking and freed up with screw driver.after cleaning everything with warm soapy water
& reassembled everything was working ok.in future I will flush out top tank once a year with warm soapy water
I had similar problem sticking impeller. There was no gunge but then my van has had little use. I would be concerned that toilet flush fluid may be the cause of your gunge. I notice the screen wash for my car had signs of gunge in plastic container stored in my garage.
We had the same problem with friends toilet , after flushing with soapy water it flushed dark gunge into toilet bowl.another thing is we don,t use addatives in toilet at home .
Some kind neighbour scrapped their van and gave me two almost full bottles of Thetford Pink & Green. Only found out later after we were getting loads of black bits in flush that old Thetford Pink was the culprit. Just about got rid of the mess now.
Thetford have changed the recipe of their later flush Pink so it's not a problem now as far as I know.
Dave.
------------- Give a man a fish and he will eat for a day,
Teach a man to fish and you can get rid of him for a whole weekend.
If the cause of the failure was toilet fluid in top & bottom tanks leaving residue then try fresh water only in flush tank & just a bio wash tab I the bottom tank. Works well enough for me & probably acceptable on sites that do not allow blue liquid.
Had same problem with sons caravan, full of gunk and stuck impeller cleaned and flushed it all out seems he never bothered to drain it (I had to show him where drain was)
Now he drains and flushes it out regularly and treats it with Milton fluid
Problem solved