Bathroom sink drain tailpiece question

[Vdawg]

Hi,
I have a question about our new (built 2022) home's bathroom sink tailpiece. I have attached two images showing the view into the tailpiece that has two holes in it on opposite sides of the tailpiece near the top where it attaches to drain flange that sits in the sink's drain hole, and another from under the sink explaining how the tailpiece sits inside the sink's molded drain hole. I understand the hole closest to the front of the sink lines up with the sink overflow tube. But there's another on the opposite side that essentially opens into the sinks molded drain area. Of course, under the sink the tailpiece has a gasket at the top where it enters the sink drain hole that stops water from that area from leaking out. But I'm wondering if that makes sense because when I disassembled it to clean it all out, it was full of black gunk that smelled bad. Water running down the drain from the sink certainly enters through those holes into the area *around* the tailpiece but still inside the sink's molded drain area (marked "RES" for reservoir in the image).

Can someone explain how this configuration isn't supposed to create a stagnant reservoir of rotting biomaterial like toothpaste and soap?
Also, since the hole in the front of the tube (sink front side) doesn't fit tightly against the sink's overflow tube (just an opening in the side of the sink's drain area), it too will collect water, and any water running down the overflow would need to fill up the reservoir area before running down the drain.
Thanks for any assistance you can provide.

 

[Reach4]

I am thinking they are not too concerned about a stagnant area, and they may not even expect that area to be aligned.

To stop the rot for now, you might remove the trap or tailpiece extension temporarily, plug/block the bottom, and add chlorine bleach to the extent that you want. That bleach can be diluted appropriately, especially if you will raise the water level to the overflow holes. Place a tub/container below, then remove the plug/block.

You could brush around with a test tube brush etc while the solution is in place.

 

[Sponsor]

 

[zomiee333]

I had the same issue with a sink installed last year. That double hole confused me too, but it’s normal. One connects to the overflow, the other just lets air circulate to prevent vacuum. The smell comes mostly from toothpaste and soap buildup.

 

[Jeff H Young]

Some how it usually isnt a problem but a bad design that seems to work good enough for many millions of lavs. plumbers just deal with it the installation and tricks to prevent leaks kare either passed down or learned through trial and error to where we get few leaks but lav pop up design and fitment to lavs is a joke just no one cares to re in vent the wheel all these parts need to fit on hundreds of lavs maybe thousands and standads are a bit loose

 

[clarajanifar]

Yes, this is normal
That extra hole lets water and air move so the sink drains smoothly. The space around the tailpiece can hold dirty water, so black gunk can build up and smell bad. Cleaning it once in a while helps. The gasket stops leaks, not dirt. Parts like this are common at Quality Plumbing Supply.