Moved a mobile home in and ran the sewer line to the main line - on some days I smell sewer gas, and I think it's coming from the vents on the house! - I want to know if I should o had put a "P" trap or something in line before hooking up to main sewer line?
I have seen other places saying to extend vent pipe on top of house up about 2' but I was checking to see if what I did so far is correct!

Sometimes mobile home workers miss the boat on running the vents through the roof and leave them open in the wall. You should have a vent from each bathroom, the kitchen and a washer vent if there is one. Check and let me know. You should not have to trap the line going to the sewer. Good luck, Tom

Some of your older houses have traps but it makes it harder to clean the line if it ever gets plugged so no you don't need a trap in the line but your vent pipe should at least be 4inch pipe for good ventilation if there is vent pipe coming out of the roof make sure it isn't plugged cause birds will nest in there and it won't vent correctly

your vent pipe should at least be 4inch pipe for good ventilation
Not quite so Scott! While 4" will give you dandy ventilation, trailers only use 3" for the main and in my area a three inch main vent is all that's required in our new home construction. Having worked as a installation plumber for mobile home factorys back in the 70's I speak from experience. Regards, n Tom