like most of us every time the car MX is washed I poked the drain holes clear with a bit of wire hanger
To me it seems to have the issue that the dirt wash just shoved back in
So today in the snow and ice I cleared mine
BUT, I used 8 cotton buds, cut the end on one side to a point, they clear the dirt, but because they are hollow, the dirt goes into the shaft, not back inside the car.
Plus being plastic less likely to harm the paint and metal.