How is blood collected for a blood transfusion?

IV bag. Blood is collected by IV into a specialized, sealed, sterile plastic bag containing an anti-coagulant. It is then refrigerated (after blood typing and testing for infections) until needed. The shelf life is 21-35 days depending on the preservative used (anti-coagulant).
About half a liter. Usually a whole blood collection is about 500 milliliters or half a liter. This is approximately 10% of a person's total blood volume, our body can handle this process without major side effects. Every healthy person that weight more than 110 lb and has 17 years of age or more is a potential blood donor, just visit the closest blood drive and save a live in just 10 mins.