Not sure there are many codes here in the mountains of New Mexico... :-)
For some unknown reason, the thread in adapter I have will not thread into the standing pipe. In fact, the thread in cap won't thread in other than a 1/2 thread. The treads in the standing pipe must be damaged.
It drains just fine as the outlet on the trailer is higher than the standing pipe. But there is a bit of water left in the drain pipe after the tanks are emptied. Need to disconnect from trailer and lift up the end and "walk the pipe" to empty it.