How do I stop my beagle from pooping in the house?

Animals don't normally foul their nests. However, once the scent is there, as far as they know, that's the bathroom. Please don't traumatise the dog by "punishing" it. This behavior may be the result of "marking" turf due to nervousness, and "punishment" will only make the animal more afraid... animals don't think the way we do...

Consider normal gastric emptying... it usually happens soon after eating. After you feed the dog, wait for an hour or so, then put the dog out, take it for a walk, nature will take its' course. Once this becomes habit, the problem is solved.