[jnaas2]

There is a reason as redwood stated that you dont use a vent for fixtures upstairs and one of them is when you flush the toilet upstairs it will more then likely pull or push air in or out of a fixture downstairs which will lead to sewer gas in you house. There is a reason for all the codes and as stated you dont need to follow them if you are not having it inspected but its sometimes easier to do it right the first time verses doing it again, the choice is yours