I feed in enclosure! I also don't really worry about them ingesting substrate unless it's that ends up making them so they can't close their mouth properly or there's a lot of substrate. Because I always dried my rats really well after thawing them, it was never an issue with substrate sticking so they rarely if ever actually ingested any. Now that they're on paper, I just squeeze the water off of them with my hand and offer - my snakes that are eating right now don't care if the rat is actually wet or dry.