On Jun 1, 2:36*pm, slakka wrote:
Dear NG,
I live in a tenement on the lower east side of nyc on the fourth
floor.
In my bathroom, both the tub and sink drain into the same
*"main drain" and get routed down from there.

Question,
what is the professional name for the "main drain"?
. The leek was in the "main drain" and I need the professional term
for it please.

Thanks in advance!

slakka

If you mean the vertical pipe that the various drains wye into, it is
typially referred to as the "soil stack".