Toilets, Sinks, Showers, Tubs and Disposals - 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?

The pipe that goes upward is probably the vent. It should connect into the main vent/drain line to complete the circuit. I see no reason for the hole and it will allow sewer gas into your home. Plug it. Good luck.