I’d try Fernox LS-X which you can get at any plumbers store or Screwfix, it’s a special silicone in a small tube to use where PTFE tape used to be used and can be used on sink bowls when adding pipe work
Just encountered the exact same grey water problem. Was your breather pipe blocked? How could you tell? How did you clear it? Thanks!
A blocked breather will typically make EVERY drain stop/slow down simultaneously, also they'll drain properly as soon as you open up the tank drain valve. Our MH doesn't have a 'breather pipe', just a hole in the very top of the tank.
Spot on, the way we use MH showers is usually very different to what we do at home due to having to be economical with water. The waste pipework doesn't typically have a trap like we have at home and R4dent posted but very often the waste pipework doesn't always fall gently to the tank for many reasons. Often a flexible pipe is used and that goes up hill at some point, you can be parked on a slope and this caused a back fall, also poor build quality too. These 'unintentional' traps collect soap deposits which dry out and go solid. If you've got a plug on the tray then leaving that in while showering and letting the water build up then letting the lot go at the end will help, an occasional power flush with the filler hose isn't a bad idea.
Sorry for delay. My black grey water tank had a recess in one bottom corner. I poked a rod up the recess which went to the top of the tank nearly and heard the air being released
If there is at least some draining taking place, enough to pour some liquid down, i'd try cheap as chips washing soda and very hot water. Can u position the van to aid draing maybe....
Don't run greasy stuff down the kitchen sink, think about ur grey tank when in use, keep it cleaner by being more careful i spose.
We used a strong dtain cleaner in a house fitted with a petspex typee bath - ruined the expensive bath. Washing soda much safer.
