One cannot willy nilly drop vitae in kegs or the sewer system and create armies of ghouls ready to do their master's bidding.
One can, however, drop vitae into a glass and hand it to the victim, thereby creating a ghoul once the victim drinks it. The mechanics for this are not for public consumption, but the characters are aware - from experimentation, their sires, or whatever - that allowing their vitae too far outside their control breaks the chain that makes the ghoul.
Does this make ghouling harder? Certainly. But it also explains why the whole world isn't ghouled.
Finally, if you are trying to ghoul a PC mortal, you must - MUST - get their permission first. If not, the whole process fails, even if you drop the blood directly into their mouths. There are a half-dozen ways to explain why that would happen, so get the permission first.