Well he didnt know where the problem was coming from. so he proposed a smoke test and then quoted me for the smoke test, redoing the trap and the vent. Then he quoted me a worse case scenario re-doing the line from under the house by tunneling under for the laundry line and installing a new washer box.
So i ended up doing my own smoke test and found the leak was coming from an angle under my house, think it is in just the general piping and not from any trap not working. But my reasoning by just installing a p trap on the main line, is if there is a seal of water from the main line, doesnt that mean that no sewage gas can come into my house??