The water is forced through the drain line through the trap, wouldn't the water be forced all the way through the trap, therefore leaving the trap dry and open to sewer gas? What is a barrel trap for and how does it work?

Thanks,
Walter

No, they are the same. I assume you mean a drum trap. Not accepted in many locations. It is a small tank that acts as a trap.

Hence the reason for a vent. The vent ensures the trap does not siphon.