The exit flaps referred to can get left in an ‘up’ position if the process of cleaning the drains is insert cleaning mechanism (rod, wire, trombone brush) from top and pull back out from top.
Exit flaps in an up position can act as noise amplifiers with the sound resonating back up the tube. The optimal method is to insert from the top (trombone brush is ideal) and pull through from the bottom leaving the flaps in the down position, obviously clear access under the car is required to achieve this.
To the OP, the RF design does seem complicated, will be interested to see what your final outcome is.