Maren
You can make something similar to the filter seen in the video with the filter of a old washing machine.I made one for the greenhouse.It is smaller but for a few square meters it is fine.For the downpipe of the garage I invested a couple of pounds and bought one used in a spraying machine behind a tractor.You can buy it as spare part and some are not expensive.Of course it needs some work to adapt it but you may be lucky and the diameter may be the same.