Waste pipe odor in garage?
I have recently pulled all the drywall in my garage ceiling and walls due to a rodent infestation. Much of the upstairs plumbing is now exposed, including the waste pipes for two toilets, a tub, shower and three sinks. The main waste line comes down a now open wall before exiting into the crawlspace. I mention all this because there is a distinct toilet odor in the garage and I am convinced it is coming from a crack or hole in a waste/ vent line. It does not smell like like septic effluent or what I think of when I think of sewage odor, it smells just an outhouse or a around a leaky toilet flange. It is definitely human, not rodent or cat. I suppose it could be a leaking flange, but we reseated the toilets a couple of months ago (because they were loose - but no obvious signs of leaking when we pulled them) and I see no water staining under the subfloor presently.
I have only owned the house for three months, so I do not know how long the odor has persisted.
How can I figure out where the odor is coming from/ if there is a crack or leak in a line? If I call a plumber, will this be a long expensive process? I am needing to close up the drywall in two weeks, so it's now or never. I definitely don't want to close up septic gas in the walls/ house.
Thanks for any advice you can give me.