I go to my Township's Monthly Sewer Meetings (which is tomorrow night) and twice in the past 3 years, though not his fault, a resident ended up w/sewage in his basement.
He has a bathroom in his basement that was added before the codes were in place. Thus, it was Grandfathered. Technically, it wouldn't pass an inspection today due to (you guessed it), venting. The path of least resistance is up through his basement toilet! And after the 2nd incident, he hasn't brought it up to code nor shut it down. I, as a resident, suggested we send the guy a letter saying that we know it's not up to code and that if it happens again, we're telling him now that the insurance company won't pay for damages. The insurance cost was $8,000, TWICE! And we, as residents, pay for it. He ought to bring it up to code or shut it down! Even if it's the Municipality's fault, he won't be covered. How many times do you have to be hit on the side of the head w/a tire iron??? (Not you personally; I'm referring to the Resident.)
Well, anyway for sure, do it right or don't do it at all. There are some things best left to a pro. My best to ya and hope this helps.