Thank you, all! Here is the Youtube three part short course on diatoms collecting and cleaning that got me started, and which more or less remains the only instruction I have been able to follow since I have exactly zero training in chemistry, and little, if any, natural intuition for it. I dream of some day taking diatom cleaning to the next level with stronger acids, fume hoods, and the like, but in the meantime am in no rush to kill myself or blow up the house. So drain "Liquid Plumr" it is for now.
Part 1 Collecting:
https://www.youtube.com/watch?v=NrhSqu8YCBo
Part 2 Cleaning:
https://www.youtube.com/watch?v=l-uN2RPvDSM
Part 3 Observing:
https://www.youtube.com/watch?v=gVI-P0AWDd4
A few more pictures...
Funny how that last bunch happened to land on that cover slip, isn't it? Just kidding, that's a Klaus Kemp 25-Form Exhibition Slide.