I found this link, The Twin-Bucket Emergency Toilet, to be the most interesting reference in the article.

It's such a simple idea, but I just hadn't thought about it before. Obvious after you read it, but easy to forget about if you haven't.

It says, if you need to set up an emergency "bucket" toilet, set up two, one for pee and one for solid waste. Urine is generally sterile, but takes up a lot more volume over time; it is, however, easier to dispose of. Solid waste is what carries the potentially dangerous pathogens and requires more care.

I got a simple camping toilet (seat, cover, outer holder and inner bucket) a few decades ago and stuck it in the attic. I was partly thinking of the big earthquake (our local most-likely big disaster) but mainly after the experience of spending one night in my house with broken plumbing and two small children. After that, I decided I didn't want to be without a backup again!