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Suppose you have 3 pipes arriving at a junction: A, B & C There are many possible water flows:

A => B+C
B => A+C
C => A+B
A+B => C
A+C => B
B+C => A
A => B (C not flowing)
A => C (B not flowing)
B => C (A not flowing)
B => A (C not flowing)
C => A (B not flowing)
C => B (A not flowing)

Obviously, given a fixed mains pressure and static valves around this junction, only one of these options can be happening at a time. But by changing what valves are open around the joint, I could switch between these various options.

In particular, I have a design where A, B, and C are all sometimes an in-flow and sometimes an out-flow.

Question: Do I need to get a "special" kind of 3 way joint for this?

If I just get "any old T-fitting" then will it handle any of these flow options, or are fittings "directional" in some way?

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    What is it you are trying to accomplish? Asking for product recommendations is frowned upon here. You might get better answers if you described your problem and goals. Commented Dec 23, 2020 at 13:34
  • I'm trying to get a direct answer to the straight forward question I've asked - do I need a special connector, to support these kinds of flow, or will "any old" connector do the job fine?
    – Brondahl
    Commented Dec 23, 2020 at 13:37
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    I also do not understand what you are trying to accomplish. Three pipes that have water which can flow any direction? HOW can the be? In home plumbing, water generally flows in one direction, from source to fixture. Valves are open or closed, they do not know what direction the water is flowing. If you want people to help then it would in your best interest to provide as much info as you can and do not take a confrontational attitude when people ask for you to explain things better. If we do not understand what you understand then HELP us understand.
    – Alaska Man
    Commented Dec 23, 2020 at 17:55
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    This is the definition of the XY Problem. Basically, you're asking about how to accomplish the solution you've chosen, when that solution may not be particularly optimal, or even possible. If you explain your entire situation, someone may be able to help you solve it in a way you hadn't thought of that may be much A) easier, B) cost-effective, C) possible, D) code compliant, E) etc...
    – FreeMan
    Commented Dec 23, 2020 at 18:08
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    Can you explain how you suspect an ordinary t-fitting would not allow for any possibility? Commented Dec 23, 2020 at 18:37

2 Answers 2

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For pressurized water or gas, any tee will work.

For gravity drains, each direction needs a different fitting.

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Get a 1-1/4" PVC T-fitting. They're cheap.

Cast "Detect magic" on it. There's no magic. (magical T-fittings are NOT cheap).

Now look at the device itself with the Mark 1 eyeball and Fingers 1.0.

Do you see anything special about that fitting?

No. There are no innards/guts which would provide any sort of flow checking. If you want, you can also examine a check valve to see an example of a piece which does have flow-management innards.

So a plain "tee" is "exactly what it says on the tin". Flow will be decided by whatever is connected to it and how.

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  • This was a lot of fun, but less actually useful than Jasen answer which clarifies that the critical difference is that pressurized water will flow in any direction and doesn't care about any "guiding" structures in the Tee
    – Brondahl
    Commented Jan 10, 2021 at 11:57

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