50 gallon was about what I was thinking. I have another problem with hot water heaters out here.
We're on well water with a high mineral content. If we are gone for a few days from our home the hot water aquires the smell and taste of rotten eggs.
It takes a volume of water to purge the lines after that.
From what I've read, it's a bacteria reacting with the anodes within the hot water heater tank itself. If I turn the water heater off, the smell is not as strong. I'm thinking about putting an electric shutoff on the new water heater.
Another solution would be to filter the water coming into the house or add chlorine.