Do I need to install a reducer from 2 1/2" to 1 1/2" for this shower drain ?

[Mini Me]

I have this shower base that I am about to install

https://www.us.kohler.com/us/ballas...d-drain/productDetail/shower-bases/429198.htm

At the bottom of that page it says it pairs well (well for them at that price) with their shower drain:

https://www.us.kohler.com/us/round-...A7B5465578A91.kohler-prod1-ecom2?skuId=360790

Specs here
https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/K-9132_spec_US-CA_Kohler_en.pdf
Here are the dimensions for it

Question: Do I need to find a way to reduce from 2" 1/2" to 1 1/2" or there is similar parts that can fit my shower pan and that match the 1 1/2" ABS pipe that I have for the drain ?

 

[wwhitney]

If you read the installation instructions for the drain, you will see it is designed to mate with 2" pipe. The 2" pipe has an OD of 2-3/8" and passes through the bottom 2-1/2" opening. Then a gasket is compressed into the annular space between the 2" pipe and the upper body of the drain.

If your plumbing code allows a 1-1/2" trap and trap arm for a shower, and that's what you have, then you'd use a 2" x 1-1/2" reducing coupling on the 2" pipe coming out the drain, and then a section of 1-1/2" pipe into the trap. The reducing coupling will take up some height, so you will need to be sure that the elevations work out.

Cheers, Wayne

 

[Sponsor]

 

[Mini Me]

Like so ?
How much vertical room do I need (I don't have a lot :-( )

 

[Mini Me]

From what I am reading I could reduce downstream of the P trap but there I also don't have a lot of room damn it

 

[wwhitney]

Yes, precisely. Or depending on your project details, you could use a 2" p-trap and a 2" drain line.

As to the height you'd need, Charlotte's catalog says a 1-1/2" x 2" reducer is 2 5/32" tall (including hubs). And that the center line of the outlet of a 1-1/2" p trap is 2-3/16" above the inlet excluding the hub. And that the insertion depth of pipe into that hub is 11/16". So along with the above drawing, you can figure out the result. The minimum height would be drain body touching the reducer touching the p-trap inlet hub, but it would be wise to assume at least a 1/4" of exposed pipe at each joint.

Can't reduce on the horizontal, it create a little dam at the bottom of the pipe. [Well, you could with an eccentric reducer, but that would be highly non-standard and probably not allowed.]

Cheers, Wayne

 

[Mini Me]

Here is a picture with some measurements
Is that a good solution?

I could try to sink the bottom piece of the P trap lower using more 1 1/2 pipe and a coupler, to make room for the coupler

 

[wwhitney]

BTW, if you could find an ABS 2" x 1-1/2" flush bushing where the outside is a smooth cylinder with the 2-3/8" OD (i.e. no larger diameter stop), and if the height of the flush bushing is no less than the height of the gasket that goes into the drain body around the 2" pipe, then you could just apply the flush bushing to a piece of 1-1/2" pipe, and eliminate the 2 x 1-1/2" reducer.

As to your picture, everything there is 1-1/2"? Is the riser in the wall the drain from a single lavatory which is wet venting the shower? And does your plumbing code allow 3 DFUs on a horizontal 1-1/2" drain (assuming a shower is 2 DFU and the lav is 1 DFU)? As well as allowing a 1-1/2" wet vent carrying only 1 DFU?

Cheers, Wayne

 

[wwhitney]

OK, a little more research shows that at least some "no caulk" shower drain manufacturers make a thicker gasket that allows you to run 1.5" pipe directly into the drain body. Eg

https://www.oatey.com/products/oatey-no-caulk-shower-drain-accessories--698610646?upc=038753421636

So if Kohler doesn't have that option, I suggest you just pick a drain from a manufacturer that does.

Cheers, Wayne

 

[Mini Me]

Yes everything is 1 and 1/2
Here is a setup we discussed here like 4-5 months ago or longer
You can find cleaner diagrams in our previous conversations
I ended up implementing your solution that eliminated a dry vent for the sink

 

[Mini Me]

OK, a little more research shows that at least some "no caulk" shower drain manufacturers make a thicker gasket that allows you to run 1.5" pipe directly into the drain body. Eg

https://www.oatey.com/products/oatey-no-caulk-shower-drain-accessories--698610646?upc=038753421636

So if Kohler doesn't have that option, I suggest you just pick a drain from a manufacturer that does.

Cheers, Wayne

So that means I have to buy the gasket and a regular dran and use that gasket ?
I can buy it online, it does not seem to require a specific drain
https://www.amazon.ca/Oatey-42163-Caulking-Schedule-No-Calk/dp/B0069KZ4LU

 

[wwhitney]

I don't recall discussing drain sizes. It would be more typical to run 2" for the shower and downstream. But if the answer to all the related questions in my earlier post is "yes," then I guess 1-1/2" is fine for a shower and a lav.

I know nothing about no-caulk drains. If the inside diameter of various manufacturer drain bodies is standard, you could mix gaskets across brands. But if they vary, you can't.

Cheers, Wayne

 

[Mini Me]

No e did not discuss the drain sizes, just the layout and the venting solution
I do remember asking me what is upstream and we concluded it was ok to drain a shower and a sink using a 1 and 1/2 drain
I am reusing a drain that served a bath tub and a sink I am just replacing the tub with a shower
Yes in that diagram everything on the left is 1 1/2. And so is in the real life picture

I am inclined more toward this solution: interjecting a piece of 1 1/2" pipe between the two elements of the P trap in order to lower the bottom side of the P trap and make room for a reducer

 

[wwhitney]

I suggest the larger gasket is a simpler/better solution. Kohler is a good brand, so their drains are probably good, but the hole size on shower basins is standardized, I believe. So there is definitely interchangeability at that level, whether or not there is interchangeability at the gasket level. If you are set on the Kohler drain, I suggest at least getting a 1-1/2" gasket and seeing if the OD matches the Kohler gasket OD.

As to your latest diagram, the US codes I'm familiar with regulate the trap seal depth, which is the measurement from the lowest point on the upper inside surface of the u-bend to the bottom of the pipe at the outlet elbow. It has to be between 2" and 4". Charlotte's catalog lists 3 15/16" center to center on a 1-1/2" p-trap, so that would be a trap seal depth of 2-7/16". That would mean the most you can extend it is 1-9/16", which would mean basically stacking a 1-1/2" coupler on top of the u-bend with a short piece of piece in there, and then the street trap outlet elbow (or using a different elbow, which would require measuring and controlling the trap seal depth).

Cheers, Wayne

 

[Mini Me]

OK I went downstairs and I have almost 3" between the floor level and the trap.
The reducing coupler is 2 5/32" so that leaves me with some room to install small segements of 2" and 1 1/5" to make the transition

I was also told I could use this. Is this something that will be permanently glued or it is a compression based coupling/transition
I think it is ABS not rubber and I thing it will be under the shower base unlike your suggested solution which can probably be replaced from above

 

[Reach4]

I was also told I could use this.

Who told you that?

I expect that is made to go into a 2 inch hub, and accept a 1.5 inch pipe. You have the equivalent of a 2 inch pipe coming down from the drain, right? So you would need a 2 inch coupling (two hubs)

plus the bushing

Then a short length of pipe into the trap.

So if that bushing goes into the shower drain, then that flush bushing would be exactly what you need. Sorry.

 

[Mini Me]

these guys over here: https://diy.stackexchange.com/quest...tch-my-1-1-2-abs-drain-plumbing/219480#219480

I asked there before asking here

 

[hj]

I am curious as to HOW you eliminated the dry vent.

 

[Mini Me]

@wwhitney was nice enough to stick with me on this and he guided me toward that final design you see here
https://terrylove.com/forums/index....-a-wall-when-the-framing-is-done.90937/page-2

 

[Reach4]

I guess the limiting factor is the pipe in the lower right of that drawing cannot be increased to 2 inch, right?

The trap arm (Trap U, through bend, through horizontal green, to santee) must be no more than 1.8 meters. You may be able to shorten that path by not drilling through the stack of 3 studs, and instead break through the wall closer to the santee.

 

[Mini Me]

Edit: the distance from the trap arm to the dry vent to the trap arm is under 4'
At a 0.25" drop per 1" that amounts to a 1" drop which is less that the diameter of the pipe (1.5")

yes that is already in the ground and I did not want to break the floor too much (I hate that part of the project)
On top of that that is the original size and it worked well with that size (and a bath tub!!) , I had not complaints
It is all cut and fitted now but I did not account for this complication with the shower drain being sized for 2"