staff KellyHenderson, From West Sussex one red star [Online] Posted 12 December 2012 by KellyHenderson Quote | Report Following several member queries regarding the water tank and flush freezing, Thetford have given the Club the following advice; Unfortunately, Thetford do not actually manufacture an antifreeze. Having said this should you feel it necessary, brands containing the following properties may be used in the fresh watertank: Ethylene glycol Mono-ethylene glycol Propane-diol Glycerol Ethane-diol Glycol Never use alcohol based anti-freeze, i.e. Methanol, Ethanol and Iso-propanol. N.B. antifreeze may only be used in toilets incorporating their own watertank, never in a unit which draws from the main water supply, i.e. the C200CS model. Post liked!