Yeah I tried to make one.
Just to make this clear I am an electrical and mechanical engineer so I do know what I'm doing!
I made a cow milking machine wanking machine
from a cow milker and gaust pump then tried a reverse compressor and finally a few shop vacs.
The reports this can be done cheap and work well are a load of crap! Cost me over $800.00
Same as my venus which by the way sent me on the mission to the cow milker sad story there
DO'NT BE FOOLED!
Ended up buying a BNG 2000 male milking machine for about 530.00 all in!
Best move I ever did!
If everyone owned one of these there would be world peace