“It's a series of tubes.”
The Noxhard Dictionary defines plumbing as the action or reaction of equal or opposite plumbers. However, the Unholy Association of Plumbers Pipefitters and Sprinklerfitters Mega-Evilish Dictionary for Humans and Their Related Ilk defines plumbing as any action performed by a real or pretend robot panda with adequate if not above-average dental insurance coverage with general or specific knowledge of pipes, piping, pipe bombs, spigots, spigoting, spigot bombs, sprinkler systems, the Theory of Water Management as it pertains to Bouncy Castles, and/or toilet floatie spring pins, not to mention taps. Even more however, laypeople generally accept that any man or beastial woman touting buttcrack credentials is automatically qualified for plumber status and any actions performed by anyone in plumber status qualifies as plumbing. All scientists all agree with all of it. Philosophers and psychologists, on the other hand, are divided on the issue. Some assert that the action of plumbing is actually an instinctual will of the mind that urges the hips and shoulders to undulate with or without the assistance of a tool known as a plunger. Others allege that plumbing is an action firmly grounded in reality and since reality has been proven not to exist, plumbing must, as an act of proper manners, also cease to exist.
edit The History of Plumbing
Plumbing was discovered in the small town of Maplestory, Mars. It was found by cosmonauts manning a 1 and 1/2 man shuttle launched by Dumbledore and his werewolf army (this was, of course, before he grew a beard). Klaus Klauserhauser and Marx Hauserklauser, the cosmonauts, drew straws to see who had to be the 1/2 man. Klaus lost. Marx said he screamed bloody murder well into the second day of the trip and when he finally died Marx had to eat him because Dumbledore didn't pack any food into the shuttle except for motherfucking earwax-flavored jellybeans.
At any rate, Marx got to Mars and learned plumbing. He kidnapped some kiddie Martians to snack on while he made the journey home. He successfully delivered the secrets of plumbing but after a brief bout of gastrointestinal pregnancy, he OMG died. A statue was erected of him and to this day it continues to be called the Loch Ness Monster. For God's sake it's not the damn Loch Ness Monster, people. I'm so fucking tired of that shit.
edit Plumbing in Space
They use vacuums. Seriously, they attach vacuum tubes to their winkies and buttholes and the tubes suck the crap right out of them. NASA engineers got the idea by being 13-year-old boys and trying to have sex with the Hoover.
edit The Act of Plumbing or To Plumb
Although the act of plumbing (or to plumb) has been widely secretified by plumberkind, there have been several documents purporting to explain the action in great detail. These documents have been eaten by grues since they were kept in a way-too-dark dark vault at the bottom of the Vatican.
Fortunately, an ailing grue was captured and killed by superglue poisoning. By dissecting this grue, scientists were able to determine that the act of plumbing (or to plumb) was once much related to today's widely popular sport of Half-Nude Tetherball. Basically, pipes are attached to other pipes to form longer pipes until the complexity of the pipes looks somewhat like an old Windows 95 screensaver. If the plumber can then ask a question on one end of this pipely configuration and receive an answer at the other end of this pipely configuration but the answer is wrong, then the pipely configuration is said to be "Bra Off." If the answer is right, it is said to be "Panty Off." If there is no answer or the answer is in some unknown alien dialect, the pipely configuration is shortened by 1/8th of an inch and the test is performed again until the pipely configuration is either 1) Shorter than 1/8th of an inch or 2) Sounding good like a motherfucker. Either way, the pipely configuration is suitable to be fitted under sinks and toilets throughout the world except for Bolivia, where, by presidential decree, all pipely configurations are "so outlawed it's not even funny."
edit Closing Arguments
Plumbers secretly defecate in your houseplants while working. And by houseplants, I mean shoes. This is speculated by marine biologists to be a way of challenging the owner of the shoe over his or her mate, which he may or may not have slept with. These challenges hardly ever escalate into a fight due to the overwhelming willingness to believe that the action is merely an act of assfoolery.