Red Tail Boa - Possible digestive problems? Please help

I have a baby male red tail boa who's only a few months old and I've only owned him for a week. He's been eating well for me every time we try to feed him but he's been having diarrhea that's been either brown and greasy or grey and almost sandy. I fed him a rat fuzzie which is a bit bigger than he's used to, on March 25th, and today he regurgitated it, then later took a very messy grey stale. I was curious if any one knows if this is anything I should be worried about. My room mate who has been raising boas and pythons for years is away this weekend and our local shop says he will be fine. But none the less, my maternal instincts make me worry about his health.

I also read online that it's possible that his body just couldn't digest all the fat and this is why he regurgitated days after eating.

None the less, if anyone has any insight, please let me know. Thanks a lot.

I meant to say "stool" not "stale". I'm not too great at multitasking while typing.

The fat probably isn't the problem. Rats are just fine.

Funny looking poops usually mean that a fecal needs to be done to check for parasites. Take a sample to your herp vet and ask for a fecal. It should run you about $50.

You said that it's eaten every time you've fed it, and you've had it a week. How many times have you fed it?

Like Eric my question is how many times have you fed him this week? You stated that you've only owned for a week but he eats well for you every time. Makes me think you're feeding it too often. I agree with Erik get a fecal done to make sure that's okay and then only feed it once in a week.

I am assuming your set-up is okay since your roommate already has boas.

I've actually owned him for a few weeks. He's been eating roughly once a week since the day that we bought him. Sorry for the confusing facts in the post.
I do have his eating records written down and they're each about a week apart but this was the fist week he ate a slightly larger rat.