PIPE SCHEMES
So, there you are, out in the backyard starting the flames of sacrifice -- a.k.a. the barbecue -- and your glance goes toward the roof, where you see an assortment of Frisbees and that badminton shuttlecock you've been missing for three years. You also see a chunk of PVC pipe periscoping out of the roof.
What is this pipe all about? Answer: sewage. Before you call Ed Norton, or your plumber, read on.
All of the stuff you flush, crush, rinse or otherwise send to a watery fate generates one heckuva lot of methane gas as it decomposes. Methane is combustible and explosive, especially if you gather up a heap of it.
That pipe on the roof is the end of a series of pipes that vent every drain in your house. The vent path needs to be clear at all times so the gases don't hang around where a spark can send you and the house into the next county. The way the venting system is kept separate -- so the gases go up into the air and you don't have to deal with them inside your house -- is by means of a trap.
On every drain or toilet, there is a trap that holds water in a way that the water acts like a lid on the vent system, so gases can't waft up through the water. You also renew the "lid" every time you add water to the system by flushing, rinsing and so forth.
The most common trap is called a "P" trap -- get your mind out of there -- because the arrangement looks like the letter "P." Actually, it looks more like the letter "U," and by all means let's not put those two letters together.
As long as you're looking up there, make sure your vent is free of bird's nests or other obstructions. Don't endanger yourself by thinking about retrieving that shuttlecock and get back to the barbecue -- make sure those ribs aren't burning!
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