If hand sanitisers have a 99.99% chance of killing germs and you wash your hands twice does that mean there's a 199.98% chance of killing germs?

Obviously.

Mathematically impossibrew

1. Put sanitizer in nostrils.
2. Snort it back.
3. Put more in, pack it full.
4. Wait for action to work.
5. ???
6. Profit.
7. No more snot.
8. Become gay
9. Become japanophile
10. Engage in nasal sex with asian man.
11. Marry said man.
12. Let man ejaculate into nostrils repeatedly.
13. Begin getting snot again.
14. Deliver snot babby 4.5 months later.
15. If ever you believe your work is done, then start back at 1.

No, they have a 100% chance of killing germs, but only kill 99% of them.