--and this is especially for Josh since Julio's already been in the game--I am still very much a rookie, so please take what I say with a grain of salt.  

Lots of great answers but if you know where the source of the odor is - just spray OdorXit Concentrate on the area.  

Or for minimal work, drill small holes near the pipe and spray foam insulation.

# of doors is generally for marketing purposes and I don't find much meaning in it, so take it with grain of salt. 

The downstairs tenant’s want me to spray insulation in the walls and ceilings as a way to mitigate the noise level and help with the heating costs.

Is there a big quality difference between using a spray gun and traditional rollers?

I'm only a low volume flipper so take my comment with a grain of salt.

I'm a realtor myself, so not offended if you take my opinion with a grain of salt.

Everything people read on BP should be taken like a grain of salt and do reach out to experts and get the real answer for their scenario to make sure they get the most accurate solution.

My 38 owns 11 houses in Salt Lake City, Utah.