Thank you for the response. They are spayed and nuttered. We actually live in Poland, so some of these products by the exact name might not be available, but I'm sure they have some kind of equivalent. I guess a trip to the vet is in order. We were pretty much told the same thing it might be...
I have two cats, one male and one female (siblings). They are both 1 and half years old. They have always used the same litter box since they were kittens. However about a 3 weeks ago my girlfriend went out of town for a few weeks on vacation and the female started doing the old #2 in the sink...
