How many fixtures on a single 1.5" PVC drain pipe?

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darmstro

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I have a basement laundry sink that is currently connected to a very old (probably galvanized) drain pipe that is buried beneath the basement floor. This pipe will not stay unclogged. There is another much newer (PVC) drain line that currently services the house's bathroom (both the tub/shower and the bathroom vanity drain through this line). This drain pipe runs vertically about 3 feet from the basement laundry sink. I'd like to cap-off the old drain line and connect the laundry sink to this newer PVC drain line. Is there any reason why I shouldn't connect the basement laundry sink to this 1.5" PVC drain line? Will a 1.5" PVC drain adequately service a tub/shower, bathroom vanity, and a laundry sink? The washing machine also empties into this laundry sink.
 
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You can plumb a bathroom sink into a 1.5" horizontal.

A washer needs a 2" line.
A bathtub needs a 2" line.
A laundry tub needs a 2" line.

You can combine the bathroom sink, the laundry tub and the bathtub into a 2" horizontal line.
Though some places like a 3" on the washer after the trap arm for suds control.
 

Geniescience

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stay tuned for more.

codes vary here and there. One thing they vary on is how many things you can combine on a 1.5" drain.

How long that drain runs is a big concern.

Since you did not mention it, you probably don't know that this is a big thing to know.
Therefore, proceed with caution. In plumbing, after you learn a little bit, you still have a lot to learn. (!).

Without having any clarity from you, I'll begin by saying that it might be possible to dump the washing machine drain water into the laundry sink, using it like a tub. And tubs DO use 1.5" drain pipe in many places. Hint hint.

Stand by.

There is more to know.

Post more information. The ball is in your court.
 

Terry

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Darmstro,
If you expect it to drain without backing up, then you should use a 2" waste line.
Laundry trays have required 2" for years.
You can use a 1.5" p-trap and trap arm, but after the vent it's 1.5"

Many older homes had 2" cast in the ground.

Geniescience,
What do you mean, more to come? Do you know something that the plumbers don't know?
Just curious, because the homeowner is asking a serious question, and you act like combining two fixtures that each need 2" and one that can use 1.25" can be combined to use 1.5"
What kind of logic is that, or are you seeing a black hole that is pulling in the entire universe in some sort of worm hole.

whirlpool_plumbing.jpg
 
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Ramon Leigh

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I could ask why the concern - if the 1.5 pipe is already too small for the fixtures attached, why worry about one more?
You're already out of code, apparently, so how much difference will one more fixture make?
It's not as though they will be used concurrently. The business about "number of fixtures" is, in a sense, rather silly,
unless there is accounting of the likelihood of concurrency. It's seems the case that not likely more than two fixtures in a bathroom are going to be used at the same time, unless you double occupy the BR.

A really dumb idea
 
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Tom Sawyer

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So, there is very little chance that someone would run the washer and the lav at the same time?

Because a thing is wrong and still works does not make it right either. Where are you going to draw that line or shall we just scrap the whole plumbing code and do whatever we want?
 
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