The secret to getting ketchup out is to give it a good shake, then hit the heel of your hand "upwards" on the top of the bottle, near where the neck meets the body (on the 57 or not, doesn't really matter). The upward force is what counts, and it somehow gets the ketchup to come out relatively smoothly. Most people strike downwards, and that's why it doesn't work. If you don't believe me, try it! Learned this trick from my uncle.

I'm guessing the functional principle here is somehow related to vacuums, those pop-tops on the new Miller beer cans, etc.