You're feeding him f/t (great!) but before you got him, did anyone else feed him live rodents?
If so, it wouldn't hurt to have his stool (a fresh sample) checked for internal parasites by a qualified reptile veterinarian. When you mention his rapid digestion, that can be symptomatic of a snake that is literally sharing his meals. (ie. he may have worms) I would wonder why he's expelling so much liquid too.
Now keep in mind that just because your snake defecates soon after a meal, it doesn't meant THAT's THE MEAL he just ate. It's probably the previous one for which he's pushing out waste products from. And snakes don't always "go" once for every meal they eat either. So keep that in mind.
Snakes that actually spend time in their water bowl may also have mites, so do be aware & check closely for any mites in or near the water bowl, & on his body. They're tiny, you have to look closely. Hopefully that's not the case, but I'm just mentioning with an abundance of caution.