hi all,
big thanks for all your help i guessed at at being 18 stone so before i put the tank on the unit me and the other half sat on it and all was ok , the tank has been there for a week now and all is ok , thanks again
you guys are all wimps. just pick up the empty tank and stand on a bathroom scale, then have a buddy fill it with water from a garden hose. subtract your own weight from the reading and tada, the weight of your tank... that's how I did it with my 72 gal anyway.