A lot of people just dump shit in the bucket when they mop or when they clean toilets. The toilet is how I discovered this harsh, horrible combination back when I was a teenager. I had the awareness to GTFO quickly though, and I generally clean with the windows open just to get the smells out anyway.The common scenario I've heard in homes is people cleaning up a lot of pet urine with bleach though I've never been clear what sort of volumes are being talked about.
Still makes me triple check before cleaning up after a pet.
Someone tossing some shit with bleach in a bucket to disinfect the floors or countertops that raw meat touched isn't unimaginable to me.