Use Cleanout for Drain

I am doing a complete bath remodel and converting a tub to a tiled shower. I understand this requires a 2" drain instead of the 1.5" that was already there. I'm also a fan of things that don't clog up as often.

My problem is that the 1.5" line enters the top of the soil pipe (in basement with full access) into a 1.5" fitting. I would prefer not to cut into the cast iron stack.

There is a 3" cleanout in the floor directly next to the soil pipe.


Is there a problem using this cleanout for the drain? I figured I would thread in a 3" pvc adapter, attach a 3"-2" sanitary wye, a new cleanout on top, and vertical 2" pipe to near the ceiling. The horizontal run would be about 12' from the shower drain trap with a single 45 degree bend along the way.

Thanks for any advice.

We do not have anything to compare sizes with, but if that is a 4" cast iron drain line, then the cleanout will be a 3 1/2" plug and there is NOTHING that you can locate which will fit it. One reason for using 3 1/2" would be to prevent people from doing what you suggest.

I have not had a chance to get back to this part of the project, and I am rethinking it. I didn't have a chance to open the cleanout, but it appears a 3" pvc threaded fitting is the correct size. I know that the correct answer is to cut into the soil pipe, splice in PVC and run a 2" line, but lets say that is not an option right now due to cost, time, equipment, ....



Which is the lesser of two evils - using the cleanout and a 2" line or just reusing the 1.5" inlet into the top of the soil pipe? Straight line from the drain to the soil pipe is about 9.5 feet. Since the inlet to the soil pipe is not pointing towards the drain location, I will have to put a bend somewhere - probably a single 45 shortly after the trap. My understanding is the best thing to do would be to reduce the 2" floor drain to 1.5" immediately and use a 1.5" trap - everything new PVC. It will not be a problem to maintain a 1/4"-1/2" slope.


A single toilet is entering from the right about seven feet away. Directly above is the bathroom sink with the vent continuing upward. The brass connection from the old tub has been removed since the photo was taken.

You do not have to "open" the cleanout. Just measure across the top of the plug, or maybe it has the size stamped on it. If measures 3 1/2" it is a 3" plug, but if it measures approximately 4", then it is a 3 1/2" plug and your question is moot, because there is no proper way you could ever use it. Especially if you tried to follow the requirement that when you do use a cleanout for a drain connection, you have to restore the cleanout somehow.

Was in a hurry and didn't have a tape handy, but had already picked up a 3" threaded pvc fitting. Overlayed on the cleanout plug it appeared to be exactly the same size. I had already picked up my other needed supplies, including:

This wye

This cleanout adapter (plus a plug)

This drain.

Along with a trap, enough pipe and elbows for the connections. Assuming the threaded adapter fits, is that the way to go?

Also, is it necessary/wise to install an air admittance valve for the shower drain?

Youve got to vent that trap within 8 feet (if using 2" trap) or 6 feet with 1 1/2 trap ( which is too small for shower drain) AND those distances are with 1/4 inch per foot slope (the minimum) But if you put more fall on the line the distance from trap to vent gets shorter! So, youve actually got more to worry about than just where to tie into the old system. Now, since I'm not there, Im going to give you advice based only on what i can see in the picture.
where i live you cant tie into that clean out (no threaded joints in drain system) but your inspector may allow it if you ask FIRST! Thread a male adaptor into the clean out female (currently in floor) Add a 3 inch tee directly above your adaptor and use the side branch for a new 3 inch cleanout. Bushing the tee down to 2 inch at the top of the tee. go vertical as high as you need to with 2" pipe. Add 90 degree 1/4 bend to turn horizontal. Run horizontal branch to shower trap at 1/4 inch per foot slope. Somewhere in this line, within 8 feet MAX of the shower trap you need to add a tee (or wye and 1/8 bend) depending on local code and add a studor vent pointing straight up and as high as you can get it (dont jam against the floor, you may someday need to unscrew it to replace it).
I Hope my description makes sense. Also, you could just call a good remodeling plumber, pay him a trip charge and pick his brain for a few minutes.

Thanks - I think I got it.

Should it be a sanitary tee or a regular tee at the interface to the cleanout? I could put the studor vent in a closet wall cavity with a vented access panel within 3-4 feet of the trap.

I need to double check my measurements since I'm going from memory, but if my 2" trap is less than 8' from the soil pipe (which is vented through the roof), can I skip the studor vent?

Im confused about sanitary tee or regular tee. when you say regular tee Im assuming your talking about waterline fittings which dont belong in the drain system. So yes, sanitary tee. Yes, you can skip the studor vent IF you are less than 8 feet in trap arm length (the pipe glued into the outlet of the trap) AND you are at 1/4 inch per foot slope and no more.
Im going to try and describe something here that may help. we're talking about the INSIDE of pipe now . Picture the outlet of the trap. The very bottom edge of the outlet can not be higher than the very top edge of the fitting where the vent connects or you are cutting off the vent. Picture a trap arm spanning 8 feet horizontally and hitting a tee in the side branch. (vent going up out of top branch drain going down bottom branch) The bottom of the outlet of the trap cant be higher than the top of the inlet of the tee. Thats why the max distance is 8 feet at 1/4 inch fall.. (on 2 inch trap) 8 quarter inches is 2 inches total fall which puts the bottom of trap outlet at same height as top of tee inlet... Any more length and the trap outlet would HAVE to be higher than the tee inlet therefore cutting off the vent.
I hope that makes sense. If not, let me know

As I understand it:

Sanitary Tee directs the flow one direction.

"Regular Tee" flows both/any direction. This fitting isn't used for plumbing at all. There is no sweep.

Of course my understanding could be wrong.

OK.. fair enuff. I'd have to say ive never had a use for a "regular" tee, and I dont see any use for it in this case either...lol .. Youre using the tee as a cleanout, to replace the one you are taking out. The sanitary tee would direct a sewer machine cable to clean out the line in the direction of the flow, and basically do the same thing as the cleanout that was there. Maybe someone might someday want to fish a cable backwards into that drain, thru the bushing and clean out that vertical line.... but i doubt it... And you could, if you really really wanted to, get a cable to do that with the sanitary tee as well.
Bottom line, I suppose you could use either one. I dont know of any code that would prohibit the "regular" one... but then again, I know FOR SURE the sanitary tee is a correct application.

OK, got it.

Just out of curiosity, would using the wye I linked in post #5 be incorrect? I used one in a similar situation a few years ago when I redid my kitchen. I had to connect to a 3" iron drain that had been cut off flush with the basement floor. I used a grommet around PVC to form a seal, then capped with the wye, a cleanout on top and a 1.5" line entering from the side. A plumber did check it out and said it was correct. I do see that liquidplumbers plan uses fewer bends, which makes sense.

While I'm at it, and have to make a trip back to the store anyway - is there any point in running a 3" drain all the way? The extra cost is minimal, and I'm all for fewer drain clogs. Should get me past the studor vent requirement also, since if I am correct a 3" line could be 12 feet from a vent???

ok.. now your in new territory.. Yes you can run 3" if you want.( cant imagine why) that being said, youd need 3 inch trap for the shower (what the heck are you washing in there anyway??) And, I dont understand why you need the extra feet that you gain from running 3 inch? How are you planning on venting this thing without the studor vent? is there some vent there that I cant see?..
As to the wye in post 5..... using it for what? I hate to say it, but im getting confused now.. lol

The iron pipe entering the top vertically of the cast iron in the photo in post 3 continues to a roof vent. There is also a sink connected. This is the view of the same pipe from the first floor.

If I understand your formula for maximum distance from trap to vent:

PipeID / SlopePerFoot = MaxDistance
2" / .25" = 8 foot
1.5" / .25" = 6 foot
3" / .25" = 12 foot

I believe my trap outlet will end up about 9 feet from the soil pipe/vent, so my options would be a 2" run with a studor vent or a 3" run without. Material cost is probably the same, but it would save me running a vent into a wall cavity, cutting an access panel in the closet, ... The basement is unfinished with plenty of space, so larger pipe is not a problem, plus if a future homeowner wants to install 12 shower heads the drain is already set.

How you gonna connect to that pipe? Seems to me that your entire reasoning for using the floor cleanout was to avoid cutting into that cast iron stack. Now your saying that your gonna get a 3 inch fitting in ABOVE where the toilet connects to that stack and use this new 3 inch fitting to run a 12 foot trap arm? The picture im looking at makes that look impossible. Isnt the top hub of that cast iron fitting more or less even with the bottom of floor joist?
Maybe I dont understand cause im looking at pictures. Question, can you tie the proposed 3 inch trap into the system UPSTREAM of where that toilet joins into the stack?

My confusion. Now I get it - I think - since I'm not entering the stack - but in the floor below the stack - that vent does not count. Ignore my reasoning above.

I'll run the 2" with a Studor vent. That toilet run is about six feet and all cast iron.

ok.. heres how to think of it.. from the roof down.. the pipe is a dry vent. point where sink connects the pipe becomes a wet vent. You can still tie a shower in ANYWHERE downstream from that point, and it is properly vented. that pipe continues thru the floor and into the basement and you can still tie to it if you want.. BUT Once the toilet connects to that system you can no longer connect anything to it unless it is individually vented. My point was that it didnt look like there was any room to break into the system upstream of the toilet and still be able to properly install a shower trap arm and get it to where it needed to go. And when youre talking about a 3 inch trap arm Im really not seeing room to put a 3 inch tee on top of that cast iron fitting and keep it low enough to get the trap arm to run below the floor joists. Am I wrong?

You are correct - there is no way to tie in above the toilet with a downward slope in the shower line.



The tee for the studor vent line must go vertical, correct? It will be a bit tricky to fit everything in, but I think I can do it.


Will this work? Sorry I am horrible at drawing, so I hope this makes sense.

The outlet of the P-trap points west. Immediately after the P-trap I will install a tee, with the vent line pointing up. The drain side will bend northwest to meet up with the cleanout. The line will slope at least 1/4" per foot.

A 90 degree elbow from the vent tee will turn south (an inch or two above the drain line). This will cross through/under a joist. Another 90 elbow will turn the line east. A final 90 elbow will turn up into a wall cavity. This line will be a total of 3 to 4 feet horizontal, then up a foot or so above the drain.

Can I run 1.5" PVC for the vent line? That will save me some space and hole cutting.

Thanks again for the help.

Alright. technically you arent supposed run a dry vent horizontally until it is a minimum of 6 inches above the flood level rim of the fixture. So if in any of that north south stuff (lol) your planning on running the vent horizontally you would be incorrect. Now, for plumbing purposes vertical is defined as 45 to 90 degrees from horizontal. So if I understand what you are saying, you can not slap a 90 degree bend on that vent line that is running vertically from the trap arm. Make sense? a 90 degree bend would make a horizontal secton of vent (no matter how short).
Heres what I would recommend.. on a section of trap arm (within 8 feet) lay a tee on its back so that the side branch points straight up vertical. cut a section of pipe that will raise the studor vent as high as possible above the trap arm but just short of the floor. Put the studor vent on top of that pipe so that its almost right against the floor. (leave just enough to thread vent in and out) Got it? This vent remains accessible from the basement correct?... if yes then its fine.

yes you can use 1 1/2 for this.
Ill be here for just a little longer.. if'n ya got anymore questions