Foul smell in one of occupied unit at a multi tenants retail

[Courtney Duong]

Hi all,

We have a 9 units retails and as of now there is 1 vacant (which should be filled up soon).  From time to time we had complaints from existing tenants that there was foul smell inside of their occupied units (only the units that are close to the vacant space).  Normally it happened after a rainy day but then was gone after that (on its own).  Or after we went in and flushed the toilets in the vacant unit (per our contractor it's because the P-trap was dry from not being used in the vacant space).  So we thought we would just keep doing this until the remaining vacant is lease out then the smell will never come back.  Well,  recently there is only this 1 tenant who keeps saying the smell is there, no matter how well they clean their unit, and even when it's not raining, and even after I go in and flush the toilets in vacant unit.  None other tenants have this issue.  I can't think of what to do or who to call for this.  Any ideas on what could be the issue or who is the right contractor to call?

Note:  one other thing I think could be the possibility is that we have 1 new tenant who is doing construction and the last couple weeks they were working on plumbing inside their unit so that could cause the bad smell?  But then the plumbing work was completed last week and the other tenant is still experiencing the foul smell now so now I am thinking that's not it either.

Any of you guys had this issue before and what did you do to remedy it?

Thanks!