Here is a quote from my review of the Evolution.
"There is a narrow channel about an inch long from the cup area back to the needle seal that might be hard to keep clean. A pipe cleaner will fit as far as the cup, but it is too large to go in the channel. The smallest brush from my airbrush cleaning kit will fit, but it's tight."
Here is another.
"When I cleaned the brush, I flushed it well with water. Then I ran my modified dental brush up the channel to the needle seal and it came out really red. I had to swab it several times. I think this would be a good practice."
Most internal mix airbrushes have some channel behind the cup. The Evolution's is extra deep. I can see why Mick swabs his. Back flushing when you clean might help.
Don