I would say if there are multiple restrooms pick one and stick to that one.

While working on the property I flushed an upstairs toilet and noticed the downstairs restroom drains gurgle.

That's like a public restroom where you bring your own toilet paper, or a restaurant where you bring your own plates and silverware. 

I have learned a lot about maintaining an elevator, fire alarm system, public restrooms, boiler system, commercial air conditioners and most of all the different laws for commercial tenants vs residential tenants.

It's an added unit to the back with an office/restroom.

I do have a septic and after doing some research it can handle at most 10 people so I just informed them they would need to bring mobile restrooms. now to see what they say...

As I'm getting up heading to the restroom my aunt (by marriage :-)) is sitting in a seat in the back now(she originally was sitting up front) smoking a cigarette.

Those nice restroom trailers rent for $1200 per weekend

I agree with @Leon D. comments about landscaping, parking lot, lighting and interior common areas such as the building lobby and restrooms. 

What is the average cost of kitchen+ restroom remodel in Orange County / Los Angeles area?