Litter box odor

I have two male cats and one litter box that I clean out twice a day. I am having trouble with a lingering urine odor near the box that I can not seem to get rid of. I have cleaned all around the area to make sure there wasn't an accident anywhere. I even went so far as to empty it and wash it with mild bleach water! Can anyone give me some advice on how to get rid of the odor?

 

The best thing you can use is a treatment product containing enzymes that litterally eat the biological matter - there are a lot of different brands, but I remember using one made by Rug Doctor that smelled really good. It's really the only thing that can permanently eliminate the urine smell because it actually removes the urine. It is poured onto the spot and allowed to dry, treating multiple times if necessary. You have to know exactly where the smell is coming from though - if it's the box, it would probably be pointless to treat it (I'd just buy a new box). If it's an area on the floor outside the box, even if you think you've thoroughly cleaned it, the enzymes should take care of it completely (and prevent the cat from reusing the area).