windyhill4.2 wrote:While i am no plumber, my understanding of pipe pitch is that too much pitch allows the water to exit too fast, which empties the trap allowing methane gas to come into the house. I never heard anything about the brown trout getting stranded with no water to swim to the pool.
Very true regarding the vent siphoning. There are required 'horizontal' run distances from a trap based on drain pipe size and also required vent sizing to keep this from happening.
Regarding pitch it should be noted that the fittings are molded so pipe that is seated properly has the 1/4" pitch. If a pipe comes out of a fitting with a lot more pitch than that you may not be seated properly and have a potential leak point.
As understand it the plumbing code only recently included a 'too much pitch' note and many places probably haven't started using the newest code...(and I can't give you a paragraph number, only going by what someone who recently went through union education classes told me at a trade show this past spring). It had only ever mentioned a minimum pitch before that. Side note...Anything over 45* is considered vertical. Also, as I have seen, the use of smooth wall plastic pipe (relative to older iron pipe) greatly reduces the supposed issue of water outrunning the brown trout causing problems. And as has already been mentioned, if it does happen the next wave of water will move the solids along nicely. It seems typical they introduce the code update when materials being used probably negate the need, but I suppose the panels that maintain the codes need something to do on their vacation conferences. I have never seen a white paper or plumbing research study done that confirms the theory of too much pitch.
I do know some cities require laterals entering mains from being too steep as they claim it interferes with the flow in the mains. But those requirements have nothing to do with solids building up in laterals.