How is everyone's teeth? (No fluoride in tank water.)
Back on topic, lots of good advice above, however whenever I use water tanks and even water jerrycans after a long period out of use. I always drain the tank (sometimes by siphon) then add a sterilising solution which in my case is often "
Milton" or even just diluted bleach solution and leave it in the tank for about an hour. After that I drain and flush the tank usually by running a hose so that the volume of water in the tank is replaced several times.
Yes I do use tank water because I'm on town water and the RW tank is usually overflowing. I also have a special food grade hose for filling.
If you are on an Enviro-Tank or similar septic system be careful not to let the hypochlorite into the bacteria tank as it will kill them as well and be careful with metals as it will corrode even stainless steel if left inside or as splashes on the outside.