[Keith]

There is a similar thread on d.org at the moment it was suggested to chop the end off where it protrudes under the car as it is a closed slit design so begins to block up from the slit first.

Personally I think that and removing them completely is a bad idea removing it will allow water in to the inner void as the drain passes through two parts of the car and cutting the end off defeats the objects of the slit design it acts as a one way valve. These drains are not that far off the ground and if open could become prone to water ingress in an upwards direction from deep puddles etc especially if entered at speed or when going through fords etc.

Also remember (in my CDT) there are two plenum drains one under the brake servo is the one that should catch most of the water but is a total pain to get at from the top. I have found the easiest way of doing either is from under the car with a bowl of soapy water on my chest to catch the muck in and a babies bottle cleaning brush that combined with hoovering out debris means it can all be done without needing to pull anything apart