How can I check if my sink drain is properly trapped and vented without opening walls?

Question

This is another question in my series of understanding my drain/sewer.

I have a bathroom sink with a p-trap that enters the bathroom wall. Underneath the bathroom is a basement where I see the pipe going straight up (from a wye in a horizontal sewer line).

Is there any way to test/confirm whether this is properly trapped and vented without opening the wall?

Answer 1

I actually learned another trick that worked: Flush a nearby toilet while listening into the standpipe. Is the flushing audible from inside the pipe? If yes, there is no trap.