Any  advice or known tried & true methods to remove odor ?

I checked all the pipes and there are no visible water leaks that I can see.The most confusing thing is that smell/odor is only in the basement vents/ducts, although the ducts run throughout the house.

Document instances of smoke odor in writing/email.Photograph evidence: butts, ashtrays.Document complaints from other tenants....

I've heard Kilz oil-based is used for pet odors but isn't it usually for wooden floors?  

We bought a foreclosure with disgusting cat urine odor.  

Those same people will have urine odor when they move out.

This also good at eliminating odors.

We bought a house to flip that smells of urine & other animal odors.  

I have found the people that grumble are the people that don't value the time they had to spend to find the deals.

It is worth its weight in gold, as any odors and grease really have nowhere to go in a small apartment.