One problem with a “central” P-trap is that if it were done that way, you’re going to get nasty smells somewhere. Sewage frequently doesn’t make it out of your house as fast as you think it will and running water down the drain changes the air pressure in the drain line to varying degrees.
The main reason it’s positioned so close to the drain opening is to accommodate venting. Every drain opening has to be vented, typically with a pipe going through the wall to a vent stack in the attic, to prevent the P-trap from being sucked dry when you do something like flush the toilet or run the clothes washer.
Ever run the washing machine and hear a sink on the other side of the house gurgling during the drain cycle? That’s because the washer draining changes the air pressure in the sewer line and the sink isn’t properly vented causing air to bubble through the the P-trap.
Ok, I don’t ever hear gurgling from other drains, so whatever they did end up doing must be set up properly. There is what looks like a capped vent that ends just a bit above the cupboard floor, guessing it acts as a buffer for air pressure to allow it to fluctuate without venting the gases into my living space.
Might be an air admittance valve. Those are usually used when venting to the roof isn’t possible or practical.
Plumbing is one of those things that’s sort of an art. You can do a whole bunch of shit wrong and have it still technically function properly. Nobody will know except you and the next person who actually knows what they’re looking at.
One problem with a “central” P-trap is that if it were done that way, you’re going to get nasty smells somewhere. Sewage frequently doesn’t make it out of your house as fast as you think it will and running water down the drain changes the air pressure in the drain line to varying degrees.
The main reason it’s positioned so close to the drain opening is to accommodate venting. Every drain opening has to be vented, typically with a pipe going through the wall to a vent stack in the attic, to prevent the P-trap from being sucked dry when you do something like flush the toilet or run the clothes washer.
Ever run the washing machine and hear a sink on the other side of the house gurgling during the drain cycle? That’s because the washer draining changes the air pressure in the sewer line and the sink isn’t properly vented causing air to bubble through the the P-trap.
Ok, I don’t ever hear gurgling from other drains, so whatever they did end up doing must be set up properly. There is what looks like a capped vent that ends just a bit above the cupboard floor, guessing it acts as a buffer for air pressure to allow it to fluctuate without venting the gases into my living space.
Might be an air admittance valve. Those are usually used when venting to the roof isn’t possible or practical.
Plumbing is one of those things that’s sort of an art. You can do a whole bunch of shit wrong and have it still technically function properly. Nobody will know except you and the next person who actually knows what they’re looking at.
It’s surprising how much depth there is to plumbing. And alarming how easy it is to become overconfident that one has it mostly figured out.