If the BP was only being offered pinky mice at the pet store (oh big surprise that is ) then it's likely been underfed. Underfed means nothing left to poop out.

Just put your snake on an every 5 or every 7 day feeding of one appropriately sized prey item (two if they total the volume of one) and you'll do fine.

Snakes, heck any animal including us, needs certain things in order to poop. They need an appropriate amount of food coming in to provide nutrition to grow on and leave something over for waste product. They need water or to get enough hydration from their prey (that prey would have to be big enough and in good shape to provide that). They need to move around to stimulate their bowels. If they have all of that...they generally will poop when they need to.

Any idea how old this snake is or it's current weight?