"Negative pressure" might be slang but it IS a term that is used. What I mean is you are generating a VACUUM as opposed to atmospheric pressure.
Is pulling air past the cups bad? Why would it NOT be bad. You are trying to get RID of air and if you are pulling it INTO the cylinders..............I...........just...........don't..........get how this could be what you want
As an old guy "I know what works" I never heard of vacuum bleeders or gravity bleeding until a few years ago. There seems to be a number of folks on here who have trouble bleeding brakes.
I'm going to guess that all this "came along" about the time that plastic master cylinders did---which cannot be easily pressure bled.
