Hence my 90mm drum brakes see some heavy use (why do street planners place pedestrian crossings and red lights right at the bottom of the best downhill courses?). The 24" front wheels also make it quite a bit harder for the brakes.
While I don't have problems with actual brake temperature, I have to clean-out the dust that gets worn off the brake pads regularly at least every two month, to keep brake performance in check. Since I prefer to ride my trike and not waste too much time with maintenance, I was looking for an easy solution.
Some velomobile riders in southern Germany and Austria use water-cooling to tackle steep descents without overheating brakes, they also mentioned an immediately improved brake performance after squirting some water into the drums. Velomobilize.at in Austria offers a water-cooling solution already, but AFAIK there are no images available.
Two weeks ago, I've installed some nipples (RC hydraulic nipples with M3 thread) into the brake plates, zip-tied a syringe to the bottle holder and tried it out. It works! Quite well actually! One or two squirts of 15-20ml of water is needed to clean both brakes.

The test rig. The left brake is water-cooled as well
Riding around with the funny syringe for a week, I've installed a water tank (RC plane fuel tank) and clyster ball 'air pump' last week.
More images in my blog post: https://etrike.wordpress.com/2018/08/13 ... um-brakes/