Bad smell in house

[focusjim]

I have a sewer smell that comes and goes daily in my house. The smell seems to be coming from the kitchen area or powder room. This smell happens usually in the afternoon to late afternoon daily. I have had a plumber in and could not find anything wrong, recommended a video. I have had the HVAC unit cleaned and ducts cleaned. The smell only lasts for a couple of hours then dissipates to no smell. This has been driving me nuts for about a year. I think I may have the answer and wanted to run this by the Forum. I have a garage in back yard about 125 feet from main house that's 9 years old. In the garage my wife has a hair salon. The sewage from garage goes to sewage pump then pumped thru the main house sewage line out the front to street. As you know there are some nasty chemicals in hair products, I was wondering if this is the answer: when the pump cycles sewage thru house it permeates up thru house in open plumbing (toilet,sink,etc.) This would also answer the intermittent smell? Any chemicals I could use to clean system?

 

[johnjh2o]

Show some pictures of where the sewer pump is connected to the mainline at the house.

 

[Jeff Handy]

Pictures, or a diagram.
And indicate slope.

 

[focusjim]

The line comes in under 6 ft. of grade into basement in rear of house next to water feed. It then goes up to meet the main from second floor that crosses to front of house and exits.

 

[focusjim]

The sewage pump from the garage has been working fine for 9 years, The slope to the house was inspected by the township at the time and approved.

 

[PerplexedPlumber]

I just posted to this discussion:
https://www.plumbingforums.com/thre...njection-vs-hydrogen-sulfide-injection.17066/
about a similar issue and one of the more obscure causes of sulfur odor.