Confused, Frustrated, Annoyed HELP!

[clrose]

Hi!
This is really my first time coming on to here and so far it looks like a really great place to ask questions and get opinions and answers so I'm hoping that I can find some help here because I'm going in circles as of now.

I have two great cats, one a 6 year old female named Mayberry and a Male 1.5 year old named Sylvester. They have both been having problems with their heind quarters for quite some time now however they seem to be completely opposite of each other, and so far I have found no answers.
The female has normal defecation like it's solid and good and everything however there is sometimes blood in the fecal matter and she has a bad habbit of rubbing her bum on the carpet. We have brought her to the vet on many occasions due to it and have been told that a) it's an anal gland infection, b) it's not enough fat in her diet, and c) she ate something to irritate the rectum HOWEVER she is on a high fat diet now and we watch her constantly and make sure there is nothing she can eat to irritate her and there is no infection to be seen. Now the male on the other hand has very runny and smelly diarrhea, he passes gas when picked up and has almost constant anal leakage, he has been to the vet and we were told that the food he's eating is okay (it's the same food as our female eats) and did all the tests and everything our vet could think of we did the whole withhold the food for 24 hours and we've withheld the water for 12 hours, and the only thing that improved the diarrhea was the with holding the water. He has no conception of being full so he will continuously eat and drink without supervision he has unfortunately not been gaining enough weight which should not be the case due to the high fat diet, and we just can not figure out what to do! Is there a problem with the food perhaps? or could there be another problem our vet just isn't thinking of?

We do also have a rat and a gecko that both the cats have access too could they be picking up some sort of bacteria from either of them?

ANY help, answers or opinions or advice would be soooo greatly appreciated!!