@Csilla VeressShort of converting to PVC, you can try some drain clearing products at Homedepot and Lowes that uses enzymes to remove the build up.

Yes, cat pee is awful, but enzyme treatment, Kilz and an ozone generator will do the trick to eliminate it. 

In a food service setting, the pest control company will often set up an automatic pump to dispense grease-eating enzymes into the trap every day.

There are some OUTSTANDNG enzyme productions on the market now.

And every 2 months I use an approved enzyme in each apartment sink and the laundry room sinks. 

I've been learning about the use of products that address enzymes but somesay it is only good for porous surfaces like carpet.

First several attempts to remove odor with enzyme cleaner have failed. 

try Nature's Miracle - it contains enzymes that break down the urine molecules. 

Try to buy a product that contains saccharomyces ferment or yeast extract or enzymes.  

The SD was $500.We had to tear out the carpet, padding, scrap up the glued down areas of padding, even remove the tack strips in areas because they were soaked, scrub the floor, put an enzyme solution down, cover with plastic, then seal the floor with two coats of Kilz before the new carpet could go in.Plus, the normal cleaning because obviously he could not clean the appliances, etc.