"TomR" writes:


What if, instead of a sink, I had a big funnel that was attached to a 15
foot garden hose. And, I put the other end of the garden hose into a 4-inch
cast iron pipe. If I pour water into the funnel (the substitute sink), I
assume that the water will just flow into the funnel, through the hose, and
into the 4-inch cast iron pipe.

The p-trap on the sink is quite different from the funnel. The p-trap
doesn't allow air through.