How to sanitize hot water tank?

[Axion]

About two weeks ago the hot water coming out of my taps has had a bit of a smell to it. Nothing major but you can definitely notice a difference from the cold water.

I did change a couple of things before the smell but I'm not sure they would have an impact. First, I am filling my fresh tank instead of using a tap feed. Its getting cold at night here in West Texas and I didn't want to have to worry about freezing a hose up. Second, I switched the hot water heater from propane to electric. I need to conserve my propane for the furnace.

I did a quick test as I have a hot water tank bypass valve in my water system. If I bypass the tank and let the water flow for a minute the smell goes away. As soon as I switch it back and hot water comes out again, the smell is back.

Now, I work in the oilfield and live in my trailer while at work. I work 4 weeks and then go home for 4 weeks. I normally drain my water system completely when I'm gone. Should I be doing something else? And, of course, any ideas on the best way to sanitize the tank?

Thanks in advance for any and all suggestions.