Anyone got any tips on elliminating grey waste tank smell. Do shower trays have waste traps fitted? The reason I am asking is that after we arrive on site the shower/loo room is a bit niffy. I am sure it's not the loo causing the smell but the grey waste tank. I always empty as much as I can but due to the way the van may be leaning it is not always possible to drain completely. It doesn't smell when setting off so I am assuming whats in there once agitated by the motion causes the smell. Has anyone tried the Thetford tank freshner, or is it just disinfectant?