Hi Ian
I would use a product by Zybax called OdourMaster it is a concentrated microbiological cleaner.
If you apply a shock dosage for three days 1:5 (ie go there and spray the problem three times) this should remove the smell at very little cost.
It would not hurt to carry on the treatment at a maintenance dosage of 1:20 until the new tennants move in better to be safe than to be sorry.
What is OdourMaster? well it is a bottle of good bactria
How does it work? well it is simply the good bactria ie OdourMaster kills the bad bactria in the urine removing the smell
It can be used on .carpets, upholstery, curtains, washrooms, floors, toilets and urinals perfect for what you need
Customer Helpline is 0800197 2882
Hope this helps

Regards Gavin