A p-trap is a device used in plumping to prevent sewer gasses from flowing up and out your drains when they are not in use. A p-trap is basically a low point in your plumbing as close to the drain as possible that will "trap" a small amount of water to form an air blockage that will prevent sewer gasses from coming up.
Generally, toilets are shaped in such a way that they act as a p-trap so one is not needed further down the line.
Generally, toilets are shaped in such a way that they act as a p-trap so one is not needed further down the line.