What makes new drum traps illegal?

Help:

My plumber says that the new "European style" drum trap that came with our new vanity set (made in China) is 'not code". I generally see that as the consense on the internet with some exceptions. But no one says why they are illegal or what the problem with them is.

Does any one know what the code failure issue is with this style trap?

http://luxaris.com/accessories.asp

Thanks

trap

It is more likely a "bottle trap", rather than a drum trap, but it is still illegal under most codes. 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. A bottle trap is in violation because it uses an internal baffle to supply the trap function, and if a hole develops in it, it will no longer serve as a trap, but the failure would not be evident so the trap could be replaced.