The water on mine will eventually dump off if enough wind comes up to billow it a little. I have a friend who made a gadget out of pvc pipe to side in between the top and the topper.
For one of my units, I used a clean paint roller on an extended paint roller pole and just walked along the side and the water came off the end I was walking toward. This slide is too high for me to do that, so it either comes off by itself or if I am ready to leave, I just bring it in a little at a time and it dumps itself.