Note: Since I only have a small multi chopper, not a blender, I do smaller quantities. I'm pretty sure a hand blender would do the trick as well. Also, personally I like it better when it's 1 part oat / 8 parts water approx (not 1/10 as shown in the video).
I mix the oat with some of the water in the multi and when it's done, I mix this content with the rest of the water in a large bowl. I also make sure that the water is cold and I stir for half a minute or so.
The cloth I use for the draining comes from an old worn out t-shirt, that is consequently very thin, and is dedicated for this use.
I find it's important to shake well the jar or bottle that the oat milk is in, before each use.
The leftovers in the cloth, either I just have them for breakfast with raisins and nuts, or I use them to make cookies.
Even if you make a mess or it doesn't work well the first time, maybe it's worth giving it another try. I think it's a super cheap experiment to make and super cost effective in the long run.