Alcohol does not make things sterile. It kills some bacteria and viruses, but by no means all.
i think this is a, if not 'the', important point. There are all sorts of pathogens that can infect us. Some love and need oxygen, others die from exposure to it (aerobic and anaerobic, respectively). Some love heat, others not so much (enter boiling water), etc., etc..
The latest evidence is there are 10x more bacteria living in our gut than cells that make up our entire body. Some of them have great benefit in our gut, but if they get in our urinary tract (for instance), they'll make us sick:
https://www.sciencenews.org/article/body’s-bacteria-don’t-outnumber-human-cells-so-much-after-all
i recently learned about the changed number from a patients spouse, who also happens to be a professor of microbiology at a local state university, after i quoted the old number of 20x to her husband lol. Which is, i believe, another good point... even scientific evidence changes. Pretty much every study i have ever read has in the summary: "more research is necessary." i see the body as an infinite universe to be explored, move over Captain Kirk.
Sorry, my point is, i believe the best advice to follow is backed by evidence, not just an authoritative attitude by someone on a kink site (even if you are 'sub' lol). To that end, i looked up a Journal of Clinical Pathology source (not just a google opinion from someone purporting to be an authority) for any interested in reading up on this topic. Caveat: this is from 1964 (i couldn't find anything more recent that was free), so the evidence is not recent, but still a lot of relevant info for those who are interested. "Bacteriological Complications from the use of Urethral Instruments: Principles of prevention":
http://jcp.bmj.com/content/jclinpath/17/5/492.full.pdf