Anything else I must do to get rid of the smoke and odor?

One thing usually leads to another and I don't want the influence or the odor permeating my units. 

You could also offer to let the offended tenant out of her lease if she is not happy.I gave one set of tenants in a duplex a stern email when I smelled it but that was mostly due to the fact that I had a vacancy in the other apartment and had a lot of prospective renters coming through for showings.The other concern here would be smoke residue messing up your paint job and leaving an odor that lingers.

This has happened three other times.I have notified the tenants to make sure they don't just throw raw trash into the bins without bagging them up first, or to not throw in tall objects like a stick which prevents the lids from fully closing, then the odor draws the creepers to the bins. 

If strong odor or surface mold is an issue, use the vinegar full strength.

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.