Venting for Drain Pipe - A thing?

[Steven B]

I just bought a duplex in March and there is washing machine hook-ups in the basement for 2 washers side by side, though they have not been used in at least twenty years. I'm now ready to hook up two washing machines, but the guy I bought the washers from looked at the existing drain pipe and said I should not run two drain hoses through it.

There is a main drain pipe which was currently being used for heating system condensate line draining which has enough space for one drain pipe. Off the main drain pipe is a second pipe elbowing out at the top above the p-trap, effectively creating a second drain pipe, which is capped. The washing machine guy said this capped pipe was for drain pipe venting, and that I shouldn't use it as a drain pipe for the second washer hose. I thought the p-trap would eliminate any need for any type of venting. Does this guy have any idea of what he is talking about, or am I good to go to remove the cap and have two hoses running down the parallel drain pipes?

 

[Steven B]

Plumbing Drain

• Steven B
• Jul 28, 2018

Drain pipe with additional drain (or vent?) pipe elbowing off the main drain pipe

 

[Geofd]

after the trap...to the right is there another tee fitting..on the same line connectionto something (vent)above or does it go directly into the main drain?????

 

[jeffmattero76]

Every drain needs a vent. Otherwise it would be like when you fill a straw with liquid and hold your finger over the top hole.

Your picture link does not work. Try posting it again.

 

[Steven B]

Here is a picture of the full system - the drain pipe and capped drain pipe in question is on the far left:

 

[Steven B]

after the trap...to the right is there another tee fitting..on the same line connectionto something (vent)above or does it go directly into the main drain?????

In the post I just added you can see the full picture and see that it goes directly into the main drain from a series of connected lateral pipes

 

[frodo]

wow......ok, do you want this done right?

 

[frodo]

do you see where the 3x2 combo is installed straight up?
that is taking up valuable space.
cut that fitting and the drain out, cut the vent pipe also.

replace it with a 3x2 wye laying on its side. install a 90 on the wye facing up.
then a tee on the 90 hang a p trap with a minimum 20'' stand pipe
View attachment 17945 View attachment 17946

 

[Diehard]

I thought you were allowed to have up to 6 feet between a trap weir and a vent(on a 2" pipe). That presently appears to be less than 6 feet.
The standpipes may have to be lengthened.

 

[frodo]

he has 2 washers, he needs 2 separate traps
each fixture requires its own trap and vent

 

[Steven B]

Excellent, thanks for all the great feedback. After looking it up, I see the purpose of vent pipes is to create an equal pressure, to allow for proper draining, and to prevent sewer gasses from coming into the home (although I thought that was the point of the P trap). So, 1) why is this "capped" vent going directly into the house - does that mean that sewer gas is venting into the basement, and 2) what is the worst case scenario if I leave it as is and put another washing machine hose drain into this capped "vent" pipe?

Does the whole thing need to be re-done with two drains and two vents, or can I get by?

 

[frodo]

the crap that is there now needs to be removed and replaced

you have 2 have 1 trap and vent per drain, the vents can tie back together like i have drawn, and connect to the existing vent system that goes threw your roof

 

[Diehard]

2 separate traps...
Yes I was curious about that, I didn't really know and couldn't find any mention of it in the code, although I didn't look real hard either.

 

[Steven B]

Alright, thanks very much for the feedback! Much appreciated!

 

[Rossando]

Worst case is every time you use the washer your floor gets flooded. Best case scenario is that when you run both machines you get a nice soapy pool in your basement! Frodo is the man follow his directions!