It's on pornhub
Not sure if I can post it here
But essentially you fill up a vacuum cup with a little bit of water
Maybe 1/4 inch
Slide your head in the cup facing DOWN
Roll the sleeve over your penis (still facing down)
Once the sleeve is securely on you now want the cup facing UP
now you pull the pin up on the cup letting the air that accumulated at the top out, at the same time press the cup DOWN INTO YOUR HEAD/PENIS
Hold your penis with the other hand to make a secure seal.
this is going to get all the air out, some water will come out as well so keep a towel close by.
Once you've gotten all the air out close the pin.
Do some manual stretches to make sure that a seal has been made.
Once it's been made you can now hang or extend at will.
There's a light film of water between the head of your dick and the plastic on the bell that cushions it and prevents blisters.