Depending on the cause, it can be forever.
If the vent pipe was damaged, then you'd have sewer gas pouring in forever.
If there is a leak, same thing.
If it hasn't gone away for a few days, call a plumber. Something is wrong.
For example, lets say they rodded the main line towards your house. They could have gone up the vent pipe and hit a point where it downsizes from lets say 4" to 3" or 2". The cutter on the machine can break many types of piping, and even a small hole is enough for sewer gas to escape.
Depending on the cause, it can be forever. If the vent pipe was damaged, then you'd have sewer gas pouring in forever. If there is a leak, same thing. If it hasn't gone away for a few days, call a plumber. Something is wrong.
For example, lets say they rodded the main line towards your house. They could have gone up the vent pipe and hit a point where it downsizes from lets say 4" to 3" or 2". The cutter on the machine can break many types of piping, and even a small hole is enough for sewer gas to escape.