Yes after the clip as the wall turns the radius is the restriction,you cannot pass a weed eater cord through it or plastic tubing..
After I flushed gallons of hot soapy water down the tube from the inside out the system always drained. I have no idea how or why but it worked all summer on our trip.
Airstream factory service was not going to de trim the interior as long as air pressure blew through the tube
I feel your pain but unless you remove cabinets and interior aluminum and insulation you will never see it.