Elvis was born on this day. He had hundreds of hits about everything from broken hearts and blue suede shoes to hound dogs and teddy bears. Even a ?hunk-a hunk-a burnin? love,? but, like many do, Elvis overlooked a biggie -- plumbing vents, an important part of plumbing in any structure. All drains connect to air vents to aid water going down the drain. As water leaves, air is pulled in through the vent, equalizing pressure and allowing drainage. Eventually, at some point, the vent goes through the roof of the house. These vents also emit smelly sewer gases which is fine until you build a roof deck or add a skylight nearby. Then, odor becomes a problem and you'll need an air-admittance valve -- a one-way device installed on the open end of a vent that only allows air to go in when needed (but not out). It traps sewer gas in and eliminates the problem. And that's the On The House tip for today.