Maybe use ESPHome on to run the servo back and forth a few times and have an automation in Home Assistant to trigger the servo when it detects the toilet running. The hard part would probably be getting power near the toilet and connecting the servo to the handle in some fashion.

https://esphome.io/components/servo/

OP I think using PCPartPicker might show you tons of options for cases with 4+ drive capacity. If you want an older case just search ebay for the options you find.

You can also mount 2.5" drives into the 3.5: trays if you wanted. Ive had my R6 for years now and just bought a 2-pack of drive caddies as it filled up to the point that I now have enough to fill the whole case.

I have a Fractal Define 6 with room for (i think) 12 HDDs. They have tons of great options for HDD storage.

Especially one without a mainstream CPU that won’t have any support

Its showing $17.97 USD for me, though I have seen process charge drastically once you actually log in.

You should really up your game and buy some ESPs and servo motors to jiggle the toilet handles when the toilets are running.