The Gemorah .זבחים כה says that the Cohen receiving the blood of a korbon must catch all the blood. That is the Dam HaNefesh - the blood flowing out of the neck.
Assuming the average cow has around 10 gallons of blood, and assuming it must lose around 25% of it to die, the Mizrak would have to be at least 2.5 gallons. This is not what I pictured, considering also that the Cohen holds it with only one hand.
Does anyone know of a source for the size of a Mizrak used in the Beis Ha'Mikdash?