Perform Smoke Test

What happens here

Insert the end of the blower hose into the opening of the unsealed roof vent. With the blower running, hold the lit smoke emitter close to the shop vac's air intake port. The vacuum will suck the smoke into its canister and blow it through the hose, pressurizing the entire plumbing vent system with visible smoke. A helper inside the house should carefully inspect all rooms, especially near plumbing fixtures and ceilings, for any sign of smoke escaping.

Goal: Find the sewer gas leak