Ghouls do not lose Vitae over time as their living body do not need it to function (they consume real food). Vampires suffer this loss of Vitae because their dead bodies needs it to function. But Ghouls do need, once a month, one dose of Vitae to keep their Ghoul supernatural properties. If they go more than one month without Vitae, they immediately start aging as per the rules described in page 500 and showing withdrawal symptoms as per the rules described on page 502 of the VTM 20th Ed. rulebook.
Now I could not find exactly where that particular one-vitae-a-month piece of information for human Ghouls is in the VtM 20th Anniversary Edition rulebook, but I did find it for animal Ghouls (which has always been the same concerning monthly vitae feeding) on page 388, in the first sentence of the third paragraph.
Now for fueling disciplines and healing, all the rules for Ghouls (including character creation) are described starting at page 496. See the "Disciplines" section for rules on Disciplines acquisition and use, the "Healing" section for using Vitae to heal damage and the "Overdosing" section for rules on the maximum number of Vitae a Ghoul can have in his system.
I may lurk a lot on these boards but my specialty (as a pen-and-paper enthusiast) is VtM. I hope that helps.
