JUNE JLC 1999 Ask anyone why drain lines are vented and you're likely to hear, "To keep sewer gas from coming into the house." And that's right — it's that simple. The water trap at each plumbing fixture is the physical barrier that keeps the sewer gas out (see Figure 1). The problem has always been how to keep the water traps intact while still allowing wastewater to drain out and vent gases to escape into the atmosphere outside the building. This is the sole intent of all the venting codes. This article will show you what happens if you don't vent properly. It's written from the perspective of a plumber who installs custom plumbing and who specializes
