Advice on drain design

[Olmedo]

I'm asking about the end of the drain line at the bottom center of the design. Am I able to use a 3" Sanitary Combo and then reduce the drain to 1 1/2" for the lav drain? That is the only fixture that will drain there. Or do I have to run the 3" line above the cleanout before reducing? Code is UPC with no applicable amendments. Thank you

 

[Plumber01]

You can eliminate the lav drain altogether.

Use the toilet vent for the lav drain. 3" Santee for a cleanout, 3x2" bushing in the top of the Santee, 2x1.5" Santee for the lav drain, 2" vent through the roof.

 

[Sponsor]

 

[Olmedo]

So it would look like this then? Seemed like it was a much cleaner run the other way. Also, the cleanout was hidden inside the lav cabinet and now it's visible between the toilet and lav.