Plumbers don't get the best PR. Think of them - what comes to mind? Their intelligence? Their "cleavage"? Their bills? Watergate?
It's no better among their peers. In my greener days as an engineer I asked a steamfitter why it was that they and the plumbers were considered different crafts. He told me "a plumber puts his nose where a fitter puts his ass".
Another craftsman assured me that all plumbers needed to know was "Friday's payday and shit don't run uphill".
Some plumbers know their place. One plumber's wife assured me that "your shit is my bread and butter".
Actually they deserve a lot more respect. Plumbing isn't just a convenience, it's an essential part of our public health programs in ways that go beyond the obvious. And it has a long honorable history.
Your plumber might not have a degree, but if he's a union journeyman he probably had a 4 year apprenticeship. And he may be licensed - here is an example of some of the stuff they need to know. It's not trivia, and it's not just about making sure your drains drain, your toilets flush, your pipes don't leak and your faucets don't drip.
For instance, if you tie your system to a public water distribution system, there is potential that nonpotable water from your system can backflow into the public system. This accounts for a lot of the concern with proper venting in piping systems, which in part minimizes the risk of siphoning.
Siphoning? How can that happen? Well, it happens every day in your toilets (I hope, anyway. Hmm, I don't think I've blogged about constipation yet...).
As for elsewhere, suppose you have a hose submerged in a bucket, then you lose water pressure at the source (if your well pump failed, for instance). If that hose was full of water, now the water will be sucked backwards through the hose into your piping system. And I'm betting that neither you nor your neighbors want to drink the water that was in that bucket.
Manufacturers play a role here. Just as pipe and fastener sizes are standardized, plumbing fixtures are often designed such that the plumbing code will be satisfied if the products are installed as directed. For instance, a faucet is to have a minimum clearance from the top of the water in a sink to prevent submerging and siphoning, so this feature will be designed in to the faucet.
If you're a do-it-yourselfer, you do well to know that the plumbing codes are there for a reason. Inspection requirements vary from jurisdiction to jurisdiction. In any case, you do well to honor the plumbing codes whether you are required to or not.
So let's give a hand to these craftsmen. Maybe they'll use it to hold their pants up.