Laundry tub drain vent pipe

I have a laundry tub in the basement that tees into a drain and then goes thru the concrete floor. If you look upwards, it looks like the drain pipe also serves as a vent pipe too. Does that make sense? Anyway, several feet above where it tees in, there is a small hole in the vertical pipe which looks like intentionally done. I now noticed soap suds would ooze out of there and run down. The laundry tub drains fine. Any ideas? Should I plug the hole up? Sounds normal?

For every pipe that goes down (Waste line), there is one going up(Vent).
The vent should go through the roof.

That is normal.
The vent shouldn't have a hole drilled in it.