You can use the vacutainer to draw blood from your survivor. You can do so as many times as you could ever want as well, but who needs blood anyway?
Well… consuming blood provides 5 to nutrition and quench. It also has a -50 to morale… however! If the survivor has the cannibal, optimist, and spiritual trait, the survivor will get a bigger morale buff than debuff, resulting in an infinite food source that makes survivors happy.
Ouroboral spirituality.
уроборос, блин :))
A sort of uroboros 
Cut off his finger and put it in the fridge: I’ll eat for breakfast.
Well, then maybe it should damage the body.
You need Leukocyte Breeder System CBM otherwise your health will drop very fast.
I have to say that being a psychopath who is perfectly happy to always be drinking your own fucking blood sounds like a feature, not an exploit.
What a hilarious exploit
Lore friendly version: the blob did it