plumbing vent and trap?

[grumpydasmurf]

What is the purpose of a vent and trap in a plumbing system?

[Rich]

Vent is to allow the traps to work properly - letting the waste go down the drain essentially without creating a vacuum in the pipe. The trap is there so sewer gases do not back up into the system and enter the house.

[roger g]

Rich is right. Without a vent or the vent in the wrong place you could by flushing a toilet or draining a sink could cause a vacuum and suck out the water in another trap which would allow sewer gases to come up. The result would be that you would have a room that smelled like my bathroom.

roger