TBH what Panthro says is true. We have two cats and coming back from being away the smell is noticeable. However, it's probably more down to the neighbourhood tom coming in and spraying in our kitchen.
We've just got a microchip catflap to prevent said tom ruining our lives, but it's a bit hit and miss with my cat (he's a big old bugger and his chip has moved a bit, so it takes some doing for the chip to get close enough to the loop in the flap).
The best thing you can do is let your cat out and stop using a tray. Failing that, keep on top of keeping the tray clean. It's the urine that stinks long term, cat turd is best dealt with straight away. Our best buy aside binning the tray altogether was when we bought an enclosed tray.