Tub Drain - Trap and fitting questions

[techinstructor]

My tub drain (from a clawfoot tub) will be located only a few inches away from the branch drain. I had my plans reviewed by the county inspector and he told me that I didn't need a vent on that drain. Since there's no vent, I'm not sure of the correct fittings to use to connect from the trap to the horizontal branch drain.

I've considered doing this.


The wye on the left will be part of the branch drain. The trap would have a horizontal pipe connected it to the 45 elbow that is connected to the wye on the right. (Sorry, I didn't have any short pipe to dry fit into the joints so you have to imagine that the pipe is there.)

The problem with this plan is that the trap weir may be more than 24" (vertical distance) from the tub drain. It may fall within the parameters, but I"m trying to have a contingency plan ready in case it doesn't.

One option I've considered is to rotate the wye, thereby raising the height of the connection. However, I'm concerned if by doing so, I would be creating some sort of S-trap.
Like this (only the branch drain location would be on the left, not on the right)


****
Another option would be to locate the trap higher up, and then use a LS 90 elbow to connect into the branch drain. However, would this not be considered an S-trap?

What is the minimum horizontal distance from a trap, before a LS elbow can turn to vertical without creating an S-trap?

Are there any other fittings that I can use to connect the tub drain to the horizontal branch without using a Sani-tee and vent?

Thanks in advance for your advice.

PS. I am aware that this pipe is over-sized (2" trap to 3" line) for the job. Just didn't think sizing up would hurt anything.

[techinstructor]

Been doing some research. Here's what I found out. Please correct me if my assumptions are incorrect.

The configuration in the second picture would be considered a p-trap with a vertical leg, as long as the horizontal trap arm is a minimum 8" long and the pipe size increases one size at the joint. It seems to me that the third option (trap w/ 8" arm then LS 90 to vertical, with increase from 2" to 3" pipe, then a combo wye into the branch drain) would also be a p-trap with a vertical leg.

I also did some reading about "wet venting" which is allowed in the NC plumbing code. I think that the inspector advised me not to dry vent the tub because of its proximity to the lav vent (within 3') , thereby making it available for use as a wet vent, though he didn't explain this at the time.

Any thoughts on this or suggestions for a way to accomplish it?

[techinstructor]

Bump

Is this just too weird or out of the ordinary? No comments? I would really appreciate hearing your thoughts on this.

[Terry]

You say the the inspector has approved the plan.

Normally a tub drain needs a vent.
The vent takes off higher then the trap arm or it becomes an S trap, which we don't install anymore.
For a 1.5" trap arm, I don't go longer then 42" before it's vented.
If you are using 3" pipe, that may be why the inspector is okay with it. The pipe is oversized, which allows some venting.

[hj]

Your tub connecting to that line means it is NOT vented and could be subject to trap loss by aspiration from the flow in the main line. IF the inspector advised doing that, then he is either very lenient or incompetent. The outlet from the trap CANNOT turn downward, regardless of the distance, until it reaches the vent. All of the "workarounds" to avoid the vent can, and may, work, but they are NOT vents, and are probably being shown as allowed by the IPC code, (which allows almost anything as long as it can be done cheaper). Using "P" traps "with a vertical leg, you would NEVER need to install vents in a house.

[techinstructor]

Thank Terry and HJ. I was really concerned about not running the trap drain to a Sani-Tee and vent. I didn't think it was right and there is a strong possibility that the inspector who will actually inspect this plumbing will not be the inspector who gave the advice (they rotate jobs in my county.) I'm going back to the drawing board to find a way to add a vent.

BTW, he also told me to wet vent the toilet, which is on a 3" horizontal drain line. I'm making contingency plans to add a vent on that line too.

[techinstructor]

We've modified the tub drain to include a sani-tee and vent. We have to use 3 elbows to "snake" the drain back down to the combo wye which connects it to the horizontal drain line. (The basement wall is 10" wide (poured concrete) and the upstairs wall is only 5 1/2" wide so the "snaking" is required to clear the basement wall and connect to the branch drain and maintain proper slope on the branch.)

Are there any problems with using this many elbows to make the connection? They are all LS's.

Top view


Side view


The three inch combo wye will be in line with the branch drain.

I greatly value your expertise and appreciate your advise. If this is not acceptable, I would appreciate suggestions for improvement.

Thanks

[Terry]

An improvement would be using a wye fitting, and then a 45, which would point to the long turn 90 going up.
We always try for fewer changes of direction.

[Tom Sawyer]

In the pictures of the first post the inspector approved them because they both dump into a 3" pipe and the trap is 2" and the tub is 1 1/2" so there will be a air space over the top of the pipe which allows the tub to vent. Personally I don't really like picture #2 because you begin to form an S trap though not really. Again because of the size of the pipe there is no way that 2" and 3" are going to be totally full and cause a trap siphon. However, if you don't need to roll the 3" wye up then don't. Your last two pictures are OK too and as Terry pointed out a wye and 1/8 bend would be more efficient but if it were me and I was within distance I would go with your first picture. It's less pipint, more direct and I like the 2" trap for the tub.

[hj]

There is nothing "wrong" with it, but a plumber would not do it that way. It would offend our sensibilities.

[techinstructor]

An improvement would be using a wye fitting, and then a 45, which would point to the long turn 90 going up.
We always try for fewer changes of direction.

I agree, but with that configuration the horizontal drain would have to be lower and consequently, too low to join into the main branch that it is headed toward at the correct slope. The height of the main branch is determined by a sleeve going through an interior concrete wall, so we didn't have a lot of leeway. ....So many variables to have to deal with.

HJ, I'm sure an experienced plumber could come up with a better way. At this point, I just want to come up with a plan that will work and meet the code requirements. Thanks for the input.

Tom Sawyer, I too liked picture number 1, but it turned out that to use that idea, the vertical drop from the tub drain to the trap would be greater than 24". I too, prefer a 2" trap for a tub and plan to see if I can get one to fit in the space available. If so, I'll definitely use that, but with the configuration shown in the last two photos Thanks for the explanation concerning the size of the pipes. It is helpful.