Landlord here, we hate 311 but it will get his attention. I wouldn't hesitate if I was in your shoes. Especially if you told him a few times. Its your only option.
If you have a legal contract & you pay on time you are in the drivers seat. Tenants have way more rights than landlords. Just dont tell the inspector when they come down about the illegal basement as that has no effect for your problems.. Will just cause him thousands of dollars worth of fines.
Let me just tell you this, if he is smart he listens to you as if an inspector comes down & your apt looks like the way you are describing they will write him up for every little thing. Outlets, holes in the wall, paint. etc etc etc