Opinions on odd drain routing for bathroom sink

[plumb_bum]

Edit: apologies for the duplicate posts, it was held up in moderation and I didn't realize it.

We are replacing the tub and I noticed something odd about the drain coming off the bathroom sink. It takes an indirect path to the main 3" line. It drains into a 2" or 2.5" line that runs parallel to the main 3" line before looping back around the end of the 3" before joining via wye. See attached photos for clarity.

Wanted to get thoughts as to why they might have done it this way. In my non-plumber mind I assume connecting to the main 3" line via combo wye would make the most sense, both in terms of flow and job efficiency. Would that have caused drainage issues or is there a code restriction that prevents such routing?

 

[Breplum]

no apparent reason. btw, the elbows are not correct either...horizontal elbows must be long sweep elbows.

 

[Sponsor]

 

[Breplum]

no apparent reason. btw, the elbows are not correct either...horizontal elbows must be long sweep elbows.

 

[Reach4]

Maybe use a closet bend. Those turn pretty tight. They connect to a 3 inch ABS pipe, and accept an inside 4 inch flange.

https://www.homedepot.com/p/Charlotte-Pipe-4-in-x-3-in-ABS-DWV-Spigot-x-Hub-Closet-Bend-ABS003300600HD/313834690

https://www.supplyhouse.com/Nibco-I058250-4-x-3-SPG-x-H-ABS-90-Street-Closet-Elbow-without-Cap-58072CL

The Push-Tite offset closet flange makes the vertical distance less critical.

https://www.supplyhouse.com/Sioux-Chief-889-GPOM-4-Inside-Push-Tite-Offset-Closet-Flange-w-Stainless-Steel-Ring-Full-Flush-1-1-2-Offset

https://www.supplyhouse.com/Sioux-C...lush-889-Series-Gasketed-Offset-Closet-Flange Either PVC or ABS version works because you are not gluing.

 

[All Shore Plumbing NY]

The routing itself doesn't look like the biggest issue to me. I'd be more interested in those horizontal turns. If they're regular 90s, I'd probably change those to long sweeps or the proper bend for the application.
Other than that I'd check that the pipe has the right slope and the venting is okay before tearing the whole thing apart. If it drains well now, I wouldn't redo the entire run just to make it shorter.

 

[Q stick]

The reason is because your tub is vented by the sink and it needed to be run this was way.

If they tied in the sink without looping around the 3”, your tub drain would be too far away to be wet vented by code.