Remove the water tank cover & peek in there.  If it's cruddy
looking, it wouldn't  hurt to wash the inside of the tank, using Dawn-
or whatever- & rinse thoroughly.

  I sanitize with chlorine bleach.  Off the top of my head  I use a
quarter cup to a tank full of water & drive around a couple days for
soak & slosh.  Then, I empty the tank using the water pump to clear
out the water lines.

   Rinse well.  If you want to, you can do the baking soda thing
again, but I don't bother.  Probably a good idea to do sanitization
annually.

George/ATL