We have noticed recently that when travelling with a cassette that is more than half full that there is a definite smell from outside our vehicle, which means we can’t travel with windows open until we have “dumped”. There is no smell in the toilet or Motorhome, and we have recently changed our SOG filter. No smell in the cassette locker. Is there something else we should be looking at. :
A spoonful (or 2) of Sod. percarbonate (such as "Napisan" or similar) should help with smell control.
You're not overdoing the curries are you?