We started doing this to downpipes several years ago , Ime a diver and had a blocked sink in the bathroom a few years ago I took the hose off the regulator put it in the sink drain put a towel around it and stuck in in the overflow then turned on the air cylinder and bingo it cleared it fine , then tried the same thing with down pipes in a customers house only problem is if the downpipes are cemented into the ground you cannot get the sods out it just goes further down the pipe , the gutter vac is a better option but the air cylinder does have its place at times . I adapted an airline hose cable tied it to a wfp with just the angle adapter on the end and cut a tennis ball in half put the tennis ball in the end of the angle adapter to fit over the down pipe hole , it will work on some gutters but on others the overhang from tiles gets in the way but it will work on some jobs