Lav and Toilet DWV Advice

Hi. I am remodeling my mother in law's master bath. I am going to replace the old CI stack with all new PVC, using no hub couplers in the attic and basement to join the new PVC to the old CI. Attached is a diagram of the way the old plumbing exists today.
Can you see anything wrong with the existing design?

Is there anything I can do now to improve it, or should I simply put the new PVC together the exact same way it exists now?

I want to use 2" PVC for the lav drain and vent pipes, instead of 1.5" which is how it is now - will that be a problem in any way? (I want to use 2†pipe instead of 1.5†cuz I assume it might drain better/faster and have less potential of clogging than the 1.5†pipe? Plus the 4†stack reducing tee’s and wyes’ I can buy here are all 2â€.)

Should I use a 45 on the lav vent to the stack (with an upside down Y at the stack), or use a 90 (with a tee at the stack) like it exists today?

Can I / should I simplify this by simply connecting the lav branch pipe directly to the stack with a Tee, eliminating the revent, and use the stack as the only lav vent? (The distance from the lav trap to the stack is about 33-34")

Is it bad that the lav drains into the stack right below where the toilet drains in to the stack?

The lav branch to the lav tee (33†to 34â€) does not appear to be sloped at all. Isn’t that bad?

The diagram shows how it exists today and they have never complained about poor drainage before. It all worked OK. I would hate to make improvements if it results in worse performance than what they had before. With one exception – every now and then (once every 1-2 years) the lav drain would run slow a little on account to hair build up. But either a couple bottles of liquid plumber or a rare visit from roto rooter would solve that for another couple years.

cleveland1 said:

Hi. I am remodeling my mother in law's master bath. I am going to replace the old CI stack with all new PVC, using no hub couplers in the attic and basement to join the new PVC to the old CI. Attached is a diagram of the way the old plumbing exists today.
Can you see anything wrong with the existing design?

Is there anything I can do now to improve it, or should I simply put the new PVC together the exact same way it exists now?

Click to expand...

looks fine the way it is

cleveland1 said:

I want to use 2" PVC for the lav drain and vent pipes, instead of 1.5" which is how it is now - will that be a problem in any way? (I want to use 2†pipe instead of 1.5†cuz I assume it might drain better/faster and have less potential of clogging than the 1.5†pipe? Plus the 4†stack reducing tee’s and wyes’ I can buy here are all 2â€.)

Click to expand...

I would stick with 1.5"

cleveland1 said:

Should I use a 45 on the lav vent to the stack (with an upside down Y at the stack), or use a 90 (with a tee at the stack) like it exists today?

Click to expand...

Wye with 45 is better and simpler.

cleveland1 said:

Can I / should I simplify this by simply connecting the lav branch pipe directly to the stack with a Tee, eliminating the revent, and use the stack as the only lav vent? (The distance from the lav trap to the stack is about 33-34")

Click to expand...

You could do it this way if you have the room. You could also pull the vent off the pipe before it connects to the stack and run your vent.

cleveland1 said:

Is it bad that the lav drains into the stack right below where the toilet drains in to the stack?

Click to expand...

That is fine. If you didn't have a vent it would be bad.

cleveland1 said:

The lav branch to the lav tee (33†to 34â€) does not appear to be sloped at all. Isn’t that bad?

Click to expand...

Do not use tee's make sure you use a tee wye.

cleveland1 said:

The diagram shows how it exists today and they have never complained about poor drainage before. It all worked OK. I would hate to make improvements if it results in worse performance than what they had before. With one exception – every now and then (once every 1-2 years) the lav drain would run slow a little on account to hair build up. But either a couple bottles of liquid plumber or a rare visit from roto rooter would solve that for another couple years.

Click to expand...

Hair build up is normal. It tends to build at the popup of at the cast iron. Your drain will be new so you should not have problems for yyears to come.

Patrick88 - Thanks much for the quick response and advice. Greatly appreciated. I would like to clarify one thing. You advise to stick with 1.5" pipe for the lav. Does it really matter, I know all that is needed is the 1.5, but I alreaday have the 2" pipe and fittings. And further, I can not find 4" x 1.5" stack wye's, I only found and bought the 4" x 2" wye's. I would rather not use a 2" to 1.5" bushing to make them connect.

So, if I rebuild it all using the 2", instead of 1.5", will that be bad, or make the drain perform worse in any way? If it does not matter at all, I will go ahead and use the 2" instead. Thanks in advance for your advice.

dwv

Is there anything I can do now to improve it, or should I simply put the new PVC together the exact same way it exists now?

I want to use 2" PVC for the lav drain and vent pipes, instead of 1.5" which is how it is now - will that be a problem in any way? (I want to use 2” pipe instead of 1.5” cuz I assume it might drain better/faster and have less potential of clogging than the 1.5” pipe? Plus the 4” stack reducing tee’s and wyes’ I can buy here are all 2”.)

Should I use a 45 on the lav vent to the stack (with an upside down Y at the stack), or use a 90 (with a tee at the stack) like it exists today?
Can I / should I simplify this by simply connecting the lav branch pipe directly to the stack with a Tee, eliminating the revent, and use the stack as the only lav vent? (The distance from the lav trap to the stack is about 33-34")

Click to expand...

As long as the sink is within 48" of the vent stack connect it to the vent with a sanitary tee

Is it bad that the lav drains into the stack right below where the toilet drains in to the stack?

No but it is not necessary if you redo as mentioned above.

The lav branch to the lav tee (33” to 34”) does not appear to be sloped at all. Isn’t that bad?

Not good, but also not terrible. Just correct it when you install the new pipe.

I have not used 1 1/2" pipe for a drain in over 55+ years, always 2" or larger, so I would advise you to stay with 2".

HJ

Thanks for the advice. I think I will simply connect the lav branch direct to the stack with a sanitary tee as you suggest, as it is less than 48" from trap to stack. Then to confirm -

1) I do not need a dedicated vent for the lav branch if I do this - right?

2) Does it matter the height that I tee the branch into the stack? Does the point that I tee into the stack need to be above or below the height of the trap in anyway? Or does it not matter.

Thanks!

Water doesn't flow uphill, so that will determine the height of the connection. Plan for 1/4" per foot, based on the outlet height of the p-trap (which is usually adjustable on the tailpiece of the sink).

Yes, thanks - DUH - I just realized how dumb that second question was.

What I really wanted to ask was - If 1/4" per foot puts me into an obstacle on the pathway to the stack (stud / header board, etc.) that is difficult to get around - then how bad would it be to make the slope much steeper, ie - is there a maximum "slopage" I need to be concerned about?

cleveland1 said:

then how bad would it be to make the slope much steeper, ie - is there a maximum "slopage" I need to be concerned about?

Click to expand...

as long and the slope from the fixture trap to the vent does not exceed 1 pipe diameter. So, if your using a 2" trap the slope can not be more than 2" overall.

Thank you all !!