I'm a wiener

I get a monthly e-newsletter from The Haunted Studio. Every month there is a contest where you have to answer a brain teaser question (I love those). From all the correct entries received, one winner is picked and that person gets their choice of any of Lew's haunted house watercolor prints (I love them). Well, the winner for January was yours truly!

Here is the question that I answered correctly:

THE PROBLEM:
You're Igor, and Dr. Frankenstein, who is up to his elbows in final assembly, hands you two empty buckets and says, "Bring me exactly two quarts of blood from the big blood tank out back!"

You know that one bucket will hold thirteen quarts and the other will hold seven quarts, but there are no markings to guide you in filling them. The buckets are heavy even when empty, and you know that with two quarts in a bucket, you can carry only one.

Clever Igor that you are, you return in time with the requisite two quarts of blood, and hand the bucket to Dr. F., who immediately puts it to its intended use. Then he turns to you, and exclaims, "Clever, Igor, you got it exactly right." How did you do it? (Hint: It took you five pours.)

Can you figure it out?

I'll post the answer later this week.