Minimum arm length for a p-trap is 3" (for 1 1/2" pipe) To me it seems impossible to slope it

[Mini Me]

So how do you slope the trap arm for a shower drain especially when the drain is close to the pipe (so the trap is min 3") As per the below diagram if you try to slope it using the arm segment that will compromise the glued connection between the arm and the trap as shown in this picture

In my case I have this. I am not sure if the part of the wye that connects to the trap arm is counted as part of the trap arm in this configuration

 

[Jeff H Young]

make sure the wye has slope. not impossible at all . you don't want the wye pointed down right?

 

[Sponsor]

 

[Mini Me]

as depicted it is possible but that weakens the junction between the P trap and the arm

 

[Helper Dave]

To get 1/4" per ft slope over 3", the difference between the high, and low point is going to be 1/16". So, as long as that wye isn't pointed down, you'll be fine. A little gravel packed under the trap will get you more pitch than you need.

 

[Mini Me]

Is the way I calculayed the lenght correct ?

 

[wwhitney]

FWIW, not sure if the plumbing codes recognize this, but as I understand it the crown vent prohibition (minimum trap arm length) should only apply to dry vent takeoffs, not to a wet vent. My understanding of the reason for the the prohibition is that it is to reduce the chance that vigorous draining will fling liquid and solids up into the vent, where they could accumulate and foul the vent. Since a wet vent is washed by another fixture that seems like a non-issue.

Cheers, Wayne

 

[Jeff H Young]

Guess it depends how pickey you or inspector is but a trap arm should have fall and a trap arm should never have back fall I think we would all agree. on a short one like that I would still like it to show a little fall at least have the bubble favoring correctly. Its pretty easy unless you glue your wye pointed down. even then you can shade the pipe with dirt or gravel and get some give in it as Helper Dave suggest

 

[Mini Me]

OK here are the result of this evening attempt to make room for a lower trap and bigger seal depth

Final result with the drain flush with the floor but there is room to move it higher when the shower base gets in its place

Here is the overall height of the assembly

And here I am making it easier to measure the seal depth by positioning the tape as needed

 

[Jeff H Young]

I suposse it dosent matter but your U bend is backward mini me

 

[Mini Me]

I suposse it dosent matter but your U bend is backward mini me

What do you mean. I did not notice and I did not know that the U of the trap is not symetrical