A drum trap is illegal because it is neither self cleaning or easy to clean. It also violates the requirement that the interior be a smooth flowing surface.Click to see full answer. In this manner, what is the purpose of a drum trap?As mentioned in previous posts, the purpose of a plumbing trap is to prevent sewer gases from coming in to a building. A drum trap does the same thing, but instead of just having a dip in the pipe to create a P-trap, a drum trap consists of an enlarged ‘vessle’ that holds a large volume of water.Subsequently, question is, why is an S trap illegal? The purpose of a trap is to prevent sewer gases, and possibly vermin, from coming in to the home. Back to “S” traps – The reason “S” traps aren’t allowed is because they have the potential to suck, or ‘siphon’, water out of the trap as the water flows down the drain. Furthermore, can you snake a drum trap? Second, the water often flows into the trap at one level and flows out at another level, making it difficult, if not impossible to run a snake from the bathtub to clear a clogged drain line. Instead, you’ll have to snake “upstream” from the drum trap toward the tub, and then “downstream” toward the main stack.How do you unclog a tub drum trap?Remove the drum trap’s cover and feed a cable auger into the trap and down the pipe flowing away from the bathtub. Turn the auger’s handle clockwise as you push it further down the drain. Once you have pushed through the clog, turn the handle counterclockwise as you retrieve the auger.