LP tank size

Pianotuna, I miss-spoke about the C-Pap my husband wired in a (not sure if it is a converter or inverter...electrically challenged here)system to run his machine...not propane. Yes we did keep the water heater on for the first couple of days then I turned it off until I needed it. I do think as was mentioned here that the dealer did not fill these tanks as he said he did.
My husband has a pretty good understanding about the purging process, I am just learning about some of these things.
Thank you for help