how to get a neighbor pay up flood damage they cause to me

[Ken Li]

My rental unit was flooded by up-stair neighbor. I saw a water mark from my ceiling over my tub.The water was get behind the wall. 

how to get my neighbor  pay for my lose out of his pocket or his insurance but he don't want to? Should  I  allow  his plumber working in my unit to fix the leak for their tub drain? What about the plumber fall ( Am I liable ?)

The condo located in San Diego CA. Any advise for newbie will be appreciated. 

Thank you!