On the being peed and pooped on issue, it just randomly happens and your gf just got lucky (unless some else has better input on the subject). On the escaping part, my personal opinion is that he's being a sneaky bastard or he might still be hungry. I have a girl that weighs similar to your BP and she eats two mouse hoppers in one meal easily.
One suggestion though: try not to handle your bp on the day of his feeding. If you handle him before you feed him, he might not eat. Definitely don't handle him after he ate because he might throw up his food. Wait at least 36 hours after his meal. I usually wait two days after feeding before handling mine.
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