well fumes go out of the bottom one and fresh air goes in the top one,simple as that,ofcourse if fumes are coming out of top one(you will get a slight bit)then its time for new pistons ect.the top pipe is only conected to the air filter so that it gets a supply of clean,filtered air .so just stick a bit of pipe on it and put one of thouse cheap small filters on it.no fumes from your engine 8)