I have been battling this problem for several months now. But I think that it has become a bit more complicated. First we noticed Drain Flies around our house. Troubleshooting led us to the drain in the floor of our laundry room. Started spraying bleach down the side of the drain, as this was one of the fixes suggested to kill future larvae..
And so, as time goes on... I notice the sewage smell from the same drain...
Have tongs, reach down inside and pull things out... have been doing this for several months... pouring bleach, etc. well, have to say that I now have pulled out of the drain, something that has been flushed from the upstairs bathroom- may have been hanging around a while, caught up somewhere, but... now I know I have a problem inside... but don't know how to address.
Please advise.

Any help> would be greatly appreciated

Remove the shower strainer and send a snake down the drain. You shouldn't have to put out over 15 feet. After load the draion up with bleach and let set overnight. Next morning flush the mess away with two large pans of boiling water. Good luck, Tom

Thanks... have tried that in the past... was a little scared today though, when I saw previously flushed item... two floors down in my laundry room...
So snaking down the toilet vs. shower makes no difference? They all connect somewhere and go from there, out of the house?

I agree with speed ball snake it first that is the most cost efficient way. Is everything backing up out of it? What's your problem inside? I had a bunch of stuff come up there my drain in my garage. And I couldn't get anything to flush, we snaked it and still nothing. We had dirt and magots coming up through there is was really... something else. Our sewage pipe had busted in the yard had to dig it up and replace it. But hopefully snaking it will do the job. If you don't have a snake there are places that will rent them for cheap.