Dumb question - why not just have one trap for the entire house?

I understand that all fixtures must have their own trap.

As a plumbing novice, I was thinking about something that I'm sure there's an answer to. If the purpose of a trap is to seal against sewer gases, wouldn't having one trap for the entire house be sufficient to do that? For example, what if on the main drain out of the house had a trap before it went into the ground? Wouldn't that trap seal off the rest of the house from sewer gases?

If there was only one trap, installation of fixtures would be easier and there would not be worries about siphoning water out of vents. I know there has to be a reason it won't work, otherwise it would be done that way.

Some reasons I can think of are that the smell from toilet waste wouldn't be sealed off from other drains. Also, don't drains allow you to clean out easier in the event of a clog or to retrieve items (e.g. earrings) dropped down a drain?

They used to have them, whole house trap, the ones I have seen were inline or running traps in 4" pipe just B4 it exited the house. The did away with them years ago.

That is a good question. I know that whole house traps were somewhat common years ago, but never (that I know of) installed today. I wonder if they often got clogged?

I don't know the real answer to the question either, but if there was only one trap and it did get clogged, your whole house could be flooded.

The main reason for multipul traps.

There are rotting waste particals in all the pipework running from all equipment that has waste water if you have ever had to clear out a trap you would notice that the pipe diameter would also somtimes be reduced due to waste clinging to the bottom of the pipes that too in causing gases,so the nasty stuff that can make you ill is just the other side of the trap.

nasty subject......

Tons of gurgling, like when a dishwasher empties into your sink line.

I was in Hallstadt in the Austrian Alps in a small B+B where the plumbing might have been done this way, all I know is that there was no P-trap on the drain for the sink in my room.

Several times in the middle of the night the sink drain produced such loud gurgling noises that I was sure I was hearing the water fall pretty far downstream in the pipes elsewhere in the house... I didn't sleep well. It did not occur to me that the whole house might have had a P-trap, and I was upset to think that the plumbing was so poorly done.

Later it occured to me that my dishwasher emptied into my kitchen sink drain without going through a separate P-trap (am I right that this is the way for most installations?), and this explained the loud noises coming out of the kitchen drain when the dishwasher was running. Do modern dishwashers make these noises too? It seems to me they are sold on the basis of their being quiet. Do they eject water silently? Do they have separate P-traps and separate connections to the stack?

Hope these two issues really are related, or else I hope to learn a lot more than I thought I would.

Oftentimes, the dishwasher drains into the top of the garbage disposal. Then drains through it. The sink has a trap, it's just that you are dumping the water above the trap. In theory, I guess, if there were crud caught in the hose from the dishwasher to the sink, that could start to smell. But, since that is pumped, the velocity is pretty high which would move that crud easier than gravity in a normal drain.

When I first bought this house (built in 1929)
- there was a lead drum trap with a lid flush with the original wood floor between the tub and the toilet that I guess took the place of P trap

The top had come loose at some point and had not been screwed back down -
above it were three layers of rotted linoleum and vinyl-
around it rotted flooring.

I vote for P traps any time

Before anyone complains about the "dumb codes" in the US, they should take a trip to some foreign countries and check their plumbing and wiring. I don't mean the so called developing countries either, Italy, Austria, Germany, and Switzerland will do. They're not totally bad, but sure not to what we are accustomed to.

(Not a pro)

To my understanding, some traps (toilets) actually require siphoning to work properly.

Solids in sewage have a different density than water, so the risk is high that they could collect on the high side of the whole-house trap, or collect on the bottom of the trap. To reliably get them through that trap, you'd need a jet to push it through, or you'd need to push a large amount of water through the pipe quickly to create a temporary siphon - just like toilets require. But then you'd need a way to refill the trap after. In essence, the whole house trap would be more reliable if it were in fact a 'whole house toilet'.

The idea I myself was wondering about.I ripped out a wall and made my bathroom bigger so relocating the tub,toilet,sink and moving the washer in there as well.I will be running 2 inch pvc starting at my bath sink onto the tub and then to the washer.From there it will run into the new main line I put in.I thought do it like this and have one pipe going to the main instead of 3.Along with this I wondered myself about in the one line going to the main putting in a trap and not having them at each fixture.There would be no solids going through the trap so curious would this work.The toilet has its own built in trap.So would it work?

Nope, can't do it.

prashster said:

(Not a pro)

To my understanding, some traps (toilets) actually require siphoning to work properly.

Click to expand...

Yes, that is why all toilets (except blowout types) are essentially s-traps.

Normal toilets (espescially the above said, siphonless blowouts) do require venting, lest you continue to siphon all the water from the trapway of the closet.

Traps at each fixture are required because of waste which collects on the interior of drain pipes. Traps are not solely there to prevent gases from the sanitary sewer. If it were that easy, we'd be going around trapping the entire house. The majority of products sent down the drains begin to degrade immediately (stink), and not everything makes it all the way out when you put it down. Traps are there not only to prevent smell, but to also produce velocity of the waste. Vents are required to maintain the water seal of the trap, and to also ventilate the sanitary sewer system.

Building traps were mainly used to prevent vermin from entering.

Drum-traps have fallen out of favor mainly because they are not self-scouring. They have a great amount of retention, and are seen as mini-septic tanks by most. They are only now used in situations where trap-arm distances are excessive and a deep trap seal is needed (dental chairs) or where they are used as an interceptor (hair and such).

lmanwarren said:

The idea I myself was wondering about.I ripped out a wall and made my bathroom bigger so relocating the tub,toilet,sink and moving the washer in there as well.I will be running 2 inch pvc starting at my bath sink onto the tub and then to the washer.From there it will run into the new main line I put in.I thought do it like this and have one pipe going to the main instead of 3.Along with this I wondered myself about in the one line going to the main putting in a trap and not having them at each fixture.There would be no solids going through the trap so curious would this work.The toilet has its own built in trap.So would it work?

Click to expand...

If you want a bubblebath, go for it. You'll definately have all kinds of crap in the bottom of the tub.

So, can a dishwasher have a separate P-trap too?

jadnashua said:

Oftentimes, the dishwasher drains into the top of the garbage disposal. Then drains through it. The sink has a trap, it's just that you are dumping the water above the trap. In theory, I guess, if there were crud caught in the hose from the dishwasher to the sink, that could start to smell. But, since that is pumped, the velocity is pretty high which would move that crud easier than gravity in a normal drain.

Click to expand...

Jim,
From what I read, you have addressed smell (crud) and how it works when it drains thru a garbage disposal.

In my case, there is no garbage disposal. Most people in my city don't have one either. Seems to be deemed unnecessary.

Who can tell me...to prevent constant NOISE, should I put a separate P-trap on the diswasher arm, and thereby bypass the sink arm altogether? Either this or find a garbage disposal (-but does that reduce noise significantly or totally?)

That would prevent the diswasher waste noise from gurgling up my sink drain. Since my kitchen is open to the living room and the entrance hallway, it would make life more comfortable.

One of the pros will chime in, but since the dishwasher is pumped, similar to a clothes washer, I think you need a little more engineering on the drain to prevent it from creating problems. The velocity of the water is going to make some noise, regardless of how you use it. Mine has a timer on it, and I set it to run in the middle of the night unless I really need something right now. You wouldn't want to blow the drain dry.

Gary Swart said:

Before anyone complains about the "dumb codes" in the US, they should take a trip to some foreign countries and check their plumbing and wiring. I don't mean the so called developing countries either, Italy, Austria, Germany, and Switzerland will do. They're not totally bad, but sure not to what we are accustomed to.

Click to expand...

I was in India in November. At the time, I had been doing a lot of plumbing work on my new house (remod of bathroom, new laundry tub, new HWH, etc). With that and my usual curiousity, I noticed the plumbing in India, Mumbai (Bombay) to be exact.
Where there was plumbing and not open trenches w/ raw sewage, the plumbing is run on the outside of the building. Obviously freezing isn't an issue there. I noticed mostly apartments, or flats, and there would be one trap for multiple fixtures. Usually one per floor. I didn't notice, or can't remember, if there was one at each fixture though. It appeared that hubbed cast iron was still common there and morter (probably among other things) was common to make the connection at the hubs.

Another interesting thing is a lot of the Indian style bathrooms have no shower pan. In the nicer places, marble is affordable. Walls and floor are all marble (large slabs) and there is a drain in the floor. One of those hand shower units are attached to the wall and water just gets everywhere. (Servants are available to clean up). Some of the more westernized homes will employ a shower curtain or door, but usually no curb.

As NG is uncommon, LP is available and used commonly for cooking and transportation, not water heating. From what I saw, electric was always used for heating hot water. They call the HWH a Geiser (they pronounce it geezer), as in Old Faithful in Yellowstone. Tankless is common as the temperature rise only needs to be a few degrees. I took many a 'cold showers' not even realizing that the Geiser was not turned on. With both systems, tank and tankless, the system needs to be turned on a few minutes before the shower is used and I was told that it would rupture if not turned off. I doubt it, but didn't want to try it!

My aunt recently got her bathroom remodeled--decided to go the tile route instead of marble. I asked her about how they put it in. Gutted the old bathroom and installed tile right on the concrete without any regard to sloping towardsthe drain. She told me getting a job done right is difficult, but getting it done so-so is easy. Poured concrete and block is the construction method of choice there for high rises, so at least rot and leaking won't be an issue. Some water can get through the cracks in the concrete, but there isn't much one can do about it if your neighbors shower is leaking into your living room--as I saw on one occasion.

Electric service was interesting too, but thats another story. I wish I had some photos of some plumbing to share w/ you all.

My stories are of the nicer areas in India. There are still many places w/o utilities and w/o running water, but those I did not visit.

Jason

lmanwarren said:

The idea I myself was wondering about.I ripped out a wall and made my bathroom bigger so relocating the tub,toilet,sink and moving the washer in there as well.I will be running 2 inch pvc starting at my bath sink onto the tub and then to the washer.From there it will run into the new main line I put in.I thought do it like this and have one pipe going to the main instead of 3.Along with this I wondered myself about in the one line going to the main putting in a trap and not having them at each fixture.There would be no solids going through the trap so curious would this work.The toilet has its own built in trap.So would it work?

Click to expand...

Not 100 percent certain about this as I have very little knowledge with plumbing, but if you use one trap for tub, sink, washer, etc., what about all of the bacteria cross contaminating from your tub and washer drain pipes, and radiating from, say your sink drain, as you're preparing to brush your teeth, getting a drink of water, washing your hands, etc? Just a thought...right or wrong someone please let me know.
Rob

1 trap serving all fixtures will not work; a kitchen sink drain pipe 2" long off a basket strainer will put off odors enough to make you feel ill, let alone numerous feet of piping open to a long distance.

Not a good idea, PERIOD.