Do you buy the Trigene ready diluted in the trigger spray bottles Debs? as that works out more expensive than buying the litre (or larger) bottle and diluting down (you can just keep refilling your trigger spray bottle). I use Trigene too, usually get a litre bottle at one of the cat shows (or you can get online too) - lasts ages, I got my last litre bottle at a cat show in July last year and I've only just finished it now, and thats filling up two trigger spray bottles each time, one I use on the surfaces and for litter trays etc at home, and the other for my grooming table and equipment.
I've used Milton fluid too, which is safe to use around cats as Ruth said. The only thing I don't like about that though, is that once you've made up a solution it needs to be used within 24 hours, whereas Trigene doesnt.
