It works moderately well. Drain absorbs life and magic, and angel blood is both of these. However, Drain pulls from a focused source, and blood is smeared in flat spots. The only way to make it work is to Drain continuously and move as if passing an invisible vacuum cleaner. Kazuya cleans the walls and floor this way, and takes a break before doing the same with the bedsheets and other places with smears. No way that he's going to walk to the laundry with a basket full of bloody sheets. He isn't creative enough to lie through that. What would the neighbours say, anyway?