Large poo is rats. Get a few different traps (they’re clever, see). Wear gloves all the time you’re handling the traps and if they’re new, leave ’em outside for a few days to weather.
The newer traps are easier to set and place, but the old style ACME snap ones work really well (gloves mask the smell of human and protect your fingers a bit.
Put the traps along runs if possible, not always easy or obvious to see them though. Close to the wall is good. Bait them with different stuff, peanut butter works well as it’s sticky and they can’t flick it off the trap easily.
They will try to chew their way out of a live trap, so you’ll hear them if you catch one. If a snap trap doesn’t kill them, they’ll make a hell of a racket too.
Best way to kill them in a live trap is drowning apparently. Fill a bin with water and chuck it in for 20 minutes.
Oh and bait a few traps but don’t set them – let the rats get comfortable around the traps for a few days before you start killing them. Don’t think that once you’ve caught two you’ve got them all – they travel in groups. Expanding foam is a good idea as they will chew through it in moments, but then at least you can see where they get in and out. Block all holes properly with concrete once you’re happy the traps are done an there’s been no activity for a week or so.