Underground downspout drainage: Water standing in my brand new drainage pipes
A backslope in a drainage line from day one is bad workmanship. Over the years it might settle a little more and become worse.
THe question is not that of harboring bugs. It's a matter of degraded capacity of the pipe.
The average homeowner who lost his house in the Oklahoma tornadoes should move for good and not rebuild. Too much complexity watchdogging the contractor. Too much a chance to be defrauded.