According to ransley :
On Jan 27, 4:29*pm, Briggs wrote:
We have a rental house that sat empty for several months. *During that
time, I left the gas water heater on the "Vacation" setting, to keep the
* pilot lit, and keep some warmth in the pipes during what passes for
"cold" weather in the NW. *Now there is a strong sulphur odor from the
hot water. *A renter has only just moved in, so I'm not sure yet if the
odor will go away with regular use. *If not, should I drain the tank, or
are there other things I should try?

If something started growing in the tank from a cool, warm temp,
getting the tank hot for a few days should kill anything, maybe 130f
-140f, turn it on high.

Greater than 140F is required to kill everything. Remember to
set it back below 140F after a few hours or a day or two. Then it's
best to get the killed goo out - there could be quite a bit.
Flushing a largish HWT will take quite a long time, so if it's
possible, drain and refill it once or twice before letting it
run for a while to flush. Draining it will also get sediment
out.

Bleach also works if you have a way to inject it. A cup is more
than enough for a HWT, let it soak for 24 hours before flushing
thoroughly.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.