What goes in, must come out (x.10)...

How can you feed a baby 2 oz. of milk and have 10 oz. come out? Our adorable daughter has a very bad habit. She poops, waits until I change her, then immediately poops again. We are going through 2-3 diapers at every changing (today with a record 4!). No kidding, she waits for me to put on a fresh diaper and instantly fills it up. Each diaper change requires me to remove her socks because it seems to be a lot of fun to stick her feet right into the dirty diaper as soon as I get it open. Also a favorite is to spit up while I am changing her so I don't have a free hand to wipe her mouth. She has such a disturbing sense of humor.