What exactly is the ptrap? What does it look like?

It's a pipe that looks like a sideways question mark.

It stays full of water to prevent gas from coming back up from the sewer.

what exactly is the ptrap? what does it look like?

A "P" Trap is a self scouring "U" shaped tubular pipe.(see image) It's function is to contain sewer gases from entering your home. If you didn't have "P" traps you would have a direct open connection between your home and the sewer. (see images).

And some folks like to call them a J trap because it is shaped much more like a J than a P.

The u-shaped piece of pipe under your sink is called a p-trap. Its design has two purposes: First, to allow the water from the sink to flow out and keep noxious gas from coming in and second, to catch items that might go down the drain (wedding rings) before they are swept away. Over time this p-trap can become plugged with hair, dirt, and other debris and the sink will start to drain very slowly, watch the video, Thankis.

John

Video (http://www.kptv.com/video/10038115/index.html)