All sewer pipes are vented using pipes that ultimately go out thru the roof of your house. Almost all of the air that you blew into your sewer pipes would go out through the vents, not down the sewer.

There are probably easier ways to vent through the roof than cutting into the sewage sytem, but, if you are intent on doing it, tap into a vent pipe rather than a drain pipe. It's a much dryer job that way, not to mention the fact that you will avoid a myriad of problems, almost all of which entail getting covered with shit in order to correct them.

PC :smokin: