No need to wait for poop. Let him have his food. He will use and lose some along the way.
Here is a photo for you. I know it isn't much but this is what a snake's tail end often looks like when they are about to eliminate. So that is completely normal. But if he has this lumpy appearance to him all the time, that can be a sure sign that something could be wrong. But to me, he sounds like a healthy, happy snake.
I took this photo because it was the first time I observed this motion and it frightened me. I thought something was wrong with my snake. But straight after, she straightened back up and sure enough, nothing to worry about.