Tapping into 3" PVC drain line

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salimajmeri

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Hello
I need to tap into a 3" drain and water line in my basement utility room to install a new washer. I was going to tap into it with a 3" x 3" x 2" sanitary tee. However, there is no flex in the 3" existing pipe for me to simply install the fitting. Do I just need to use a couple of 3" flexible rubber couplings to attach the fitting (with some 3" PVC) to the existing pipe? Something like this coupler (Fernco 3 in. x 3 in. PVC DWV Mechanical Flexible Coupling P1056-33 - The Home Depot)

I would put it right below the cleanout plug.

Would the use of these couplers be in accordance to code?
 

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Thank you. I'll get those.

Would that main 3" line not already be vented? Are you saying I would need to separately vent the new 2" line?
 
salimajmeri said:
Thank you. I'll get those.

Would that main 3" line not already be vented? Are you saying I would need to separately vent the new 2" line?
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Your 2” trap for your washer must be vented. Having the entire house above flushing through that 3” vertical pipe past your 2” trap would be improper. There would need to be a vent placed between the ptrap and the main stack. 2 pipe diameters, 4” in this case must be maintained between the trap outlet and the new vent.

This is the proper way that meets code.
 
You may have seen something like this on the internet. This is WRONG!!!

1689122760234.png

Pretend the wash sink in the basement is your washer. The following is one proper way to vent a P-trap in the basement. You could also take the vent off the basement P-trap up through the roof if you don't have good access to the vent stack,


1689122717670.png
 
Got it. Thank you! So something like the attached picture with my scribble. Can I vent to the side of the house or does it have to go to the roof? Alternatively, can I use an air admittance valve like the second picture instead?
 

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To meet code you would need to run the vent above the roof or connect to a dry vent existing in your plumbing system.

The studor vent is a no go.

Does this portion of pipe I marked in yellow have water flowing if you run all the fixtures upstairs ?
1F357C5E-C910-42FF-82EE-02D0B5B84023.jpeg
 
Is the "studor vent" a no go because it would be buried in the wall ? If it was outside of the finished wall (accessable) would it be ok ?
 
salimajmeri said:
I will check and report back. Thank you for the info so far
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So it's very hard to tell which pipes the water is coming through from upstairs. I stick my ear to it and it sounds like all of them (even when only one sink is on).

I pulled back the insulation a bit more to figure out where things are going and took a picture attached.

The red pipe is going up to the first floor and not sure where it goes from there.

The green pipe goes up to the first floor, and I'm assuming it goes to one of the bathrooms or kitchen.

The blue pipe definitely goes to the existing basement bathroom and there is a pipe connecting to it from the first floor bathroom (you can see the ptrap from the toilet above in pink).

Here is how my house is currently laid out.
Basement (1 finished full bathroom just to left of these pipes)
First floor (1 full bath and 1 half bath right next to each other right above all these pipes. Kitchen is on the other side of the house)
Second floor (three full bathrooms, of which one is directly above the bathroom on the first floor)

If that pink colored ptrap in my picture is for a toilet, the only pipe that could be it's vent is the red pipe, correct? I don't understand why the red pipe doesn't go straight up. I thought vent pipes should be vertical the whole way through.
 

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Run hot water in all your upstairs fixtures having hot water and see if that pvc marked in red gets hot above where the others connect to it. It might be best if you felt the horizontal portion, way up top.
 
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Ludington said:
But isn't that what it was made for ? Can you elaborate just a little why it's not acceptable ?
Just trying to learn something here.
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Typical studor vents let air into the system under negative pressure. With a fixture at the bottom of a stack it could and most likely would be subject to positive pressure. This can blow water out of the ptrap.
 
Twowaxhack said:
Run hot water in all your upstairs fixtures having hot water and see if that pvc marked in red gets hot above where the others connect to it. It might be best if you felt the horizontal portion, way up top.
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Yep. I ran the hot water on the 2nd floor sink on HOT. That red colored pipe (from my picture) is the only one that got hot, first along the horizontal portion, and then also on the vertical portion.
 
salimajmeri said:
Yep. I ran the hot water on the 2nd floor sink on HOT. That red colored pipe (from my picture) is the only one that got hot, first along the horizontal portion, and then also on the vertical portion.
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Technically you can’t use any of those pipes for a vent.
 
salimajmeri said:
Understood. What is my best option then?
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If you want it done to meet plumbing code you’ll need to run a new vent and either go out your roof or connect to a vent in the attic.

You could check the other pipes but it’s a good chance they’re all drains.
 
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