Trap arm size vs. santee size

[ejg]

I searched the internet but couldn't find an answer. Can you connect a smaller trap arm to a larger sanitary tee opening? The sanitary tee opening to the trap arm is 2" but the decorative trap arm, which serves a lavatory, pedastal sink is 1 1/2". Is this going to be a problem?

 

[Smooky]

The trap arm must be twice the inside diameter of the pipe.
This little guide explains it well:
Plumbing-and-Trenching-for-Homeowners---2018 (klickitatcounty.org)

 

[Sponsor]

 

[ejg]

The trap arm must be twice the inside diameter of the pipe.
This little guide explains it well:
Plumbing-and-Trenching-for-Homeowners---2018 (klickitatcounty.org)

Nice guide! Thanks. I understand that the trap arm must be twice the inside diameter of the pipe, but my question is about something different. I'll try to phrase it another way. Can the diameter of the trap arm (in this case 1 1/2") be a smaller than the opening diameter of the sanitary tee (in this case 2")? The diameters of the 2 are mismatched. Is this a problem?

 

[Smooky]

You can do that

 

[ejg]

You can do that

Any advantages or disadvantages?

 

[Smooky]

It depends on how much space you have to work with and whether it is going to show or not .
How do you plan to put it together?

 

[Terry]

You can use a flush bush to reduce from 2" to 1-1/2" at the santee. Then you can run your 1-1/2" trap arm.