For a BP to defecate the BP needs to have waste to eliminate, the frequency and amount will depends on several factors, the animal itself, prey size and feeding frequency.

If you are feeding pink and fuzzy mice, you are UNDERFEEDING your BP, even an hatchling out of it's egg can start of on mice hoppers and can quickly move to adults.

A rule of thumbs for hatchlings and juvies is to feed a prey equal the girth size of the animal which is the widest part of your BP's body (no need for a scale).

Adult feeding is different since their metabolism is different as well.

Keep in mind that a growing BP will utilize most of the prey item for it's growth.