I keep it closed, or try it, maybe I need a door closer ...
I changed it three days ago.
I need to check the UTI thing.
I'm no expert, so take my info with a grain of salt, since it's restricted to my experiences with a cat I had a few years ago who was peeing in/on odd places.
1. She was highstrung, to begin with. Part Siamese.
2. She once peed on the dining room table when workers had been here for hours making banging noises. She got upset, I guess.
3. Changing your litter box every 3 days sounds long, to me. I learned that I had to clean up her clumping litter every day, add more litter, and then do a full change-out of litter once a week. She did NOT like a dirty litter box. (Also, the other poster is correct about how much litter. I learned that having a lot of litter was something she didn't seem to like.)
4. It matters how convenient the litter box is. If there's one litter box and it's at the back of the house, so that your cat has to go across the house to urinate, that might be too inconvenient.
5. My dog, I learned, was getting into her litter box.
Once I kept the dog out of her litter box (I got a litter box with a top so that it was harder for the dog to stick his head through, and I started strict training the dog to stay away from it; later I was able to remove the top, and I set up a room divider with just enough space for her to squeeze through but not the dog), AND started cleaning her clumping litter daily with a full change out of litter weekly, and moving the litter box to a more convenient spot....the "accidents" stopped happening.
I took her to the vet, of course, to make sure she was healthy. She was. I never had these problems with two other cats I had. But that little Siamese was just highstrung, so more sensitive to these things. Humans are all different, too, aren't we?