I have a few questions so here goes...

Do you need to keep litter trays (or decrease the number of trays) in the house if you have a cat flap?

Are cat flaps even a good idea?

I have three cats, does this mean I need one tray per cat plus an extra for each cat then I'd need five trays and if I had five cats that means I'd ned nine? *gulp*??

Will cats still toilet outside if they havn't got a cat flap but you let them out?

Please don't pick up too much on my hint of five cats, it's just a friend of mine just took on two kittens and her little boy is allergic to them so she sort of offered me them.....
Don't people know I'm vunerable !! :lol3: :rolleyes:

The rule of thumb is one box per cat then only 1 extra. So with 3 cats, 4 boxes. With 5 cats, 6 boxes.

I can't answer your question about cat flaps. Most of my cats are indoor only (too vulnerable to roaming dogs here). I do have 2 (semi-feral) cats that are savey enough to go outside and I'm simply their doorman. In the winter they will ask to go outside, do their business, then beg to come back inside. Their preferance is to go outside for their business, but then there are other indoor only cats that keep me busy scooping their litter, and I think they would rather not compete for the litter boxes.

Re flaps. We have a flap, the girls come and go as they please. Much of the time they prefer to do their business outdoors, but they certainly do use the boxes indoors. In previous times, prior to the flap, our cat(s) have done pretty much the same -- some out and some in -- the flap doesn't seem to make much difference to that dynamic, just reduces the "doorman" duties.

My sister had 1 box indoors for 7 cats, they normally did their business outside so 1 was enough for overnight when the cats were shut in.