I guarantee you, depending on the tenant, the invoice will be higher the there deposit, let them challenge it, they will lose every time.As per the urine smell, I bought a run down 8 unit apartment building, each unit was so bad the 1st thing that burned where your eyes, the 2nd was your lungs from the smell, each and every unit.Pull the carpet and padding, then go take a shower, its grouse, then wash walls with heavy bleach water, then pour and scrub heavy bleach water in to sub floor until it is soaked. open windows let dry and air out for a few days.

But in March the upstairs tenant calls us again and says that her washing machine is not working.

I understand the posts saying to simply cut ties and wash your hands of the mess and move on. 

Back in the day I knew guys who would go down into the Pine Barrens of Jersey with tankers full of waste solvents, find a lonely road, and dump their load. 5,000 to 8,000 gallons a shot

Treat it like a washing machine.

Then use a clean product or method targeted for that type of odor.We clean all hard surfaces with a cleanser/degreaser, then a vinegar wash, and finish off with a disinfectant. 

While it's not close to the Univ of Wash, it wasn't far, and it was less expensive for the students to live in that apt than to live closer to the University.

All he knew was he was getting his rent each month.  

Unless you would need to pay more taxes on a portion because it bumps you up a bracket, wouldn't this be a wash as far as taxes?

Got the payment for the eclectic bill from the tenant next door at the same time and then went over to check on the new house we are putting in a couple miles away to see how much of the newly made pad and gravel drive had washed out.