If you give someone a swirly, you risk exposing them to harmful bacteria from the toilet water. Is there any way to clean a toilet super thoroughly beforehand to make it safe?
If not, if someone hypothetically installed a toilet in their basement that no one used for its intended purpose, would that be safe to use for swirlies? Particularly if you let it feed from an isolated water tank instead of the house plumbing and drain into another tank.
You’d have to send it to a lab.
Bleach is literally going to kill everything in there. The bottle says 99.99% of bacteria and viruses only for legal reasons. Really it kills 100% when used properly.
Just bleach it twice, use a brand new scrubbing brush, hit the outside of the bowl and every little crevice you can see and you’ll be good to go.