We get a sewer gas smell in our laundry room. It is much stronger after we do laundry. We started getting the smell after the builder moved the vent stack. It had to be moved because it was too close to the fresh air intake for the whole house air purification system. We don't want to do a regular smoke test to check the vent for leaks becuase my wife is extremely sensitive to chemicals and it would be very difficult to remove the smoke residue if there is a leak in the vent stack. The vent stack for the laundry room is the closest one to the septic tank, in case that's relevant.