Where the rubber seal is on the bottom of the neck, that's where I set mine to normally.
Around the purple line is where I set mine, seems to produce some stinky dark skimmate that isn't too watery.
Videos? Id be happy with a instruction manual!
I will be happy to help anyway I can. It is a great skimmer for small tanks. What do you guys want to know? No,bI don't work for them but I've dealt with many skimmers over the years.