I've put together some scripting for Domoticz which converts depth and temperature readings into virtual sensors for tank full percentage and volume — compensating for fuel expansion and reporting the volume at a canonical temperature so you don't get lower readings overnight.

What I need to do next is automatically feed the data from rtl_433 into Domoticz. Some people have scripts for that, but I think Domoticz should spawn rtl_433 in its mode which outputs JSON, then just read data from its stdout.

I also need to fix the volume sensor. Currently I'm abusing a water meter sensor type, since that was the only one with the correct units (albeit misspelled). But the graphs don't do the right thing there because they plot usage as the volume increases, and we want the opposite. And we also want to plot the absolute volume over time and project when it'll hit zero — not something we have to do with a water meter.