[Travelling Three]

I have a 2017 Montana 3661RL. Contained in the outside "control panel" is the multi-function Anderson water switch that when switched into the correct position will fill the fresh water tank. I call it an Anderson switch because that's what Heartland calls it. I know of no way to add any cleaner or sanitizer to the fresh water tank to clean/sanitize the tank. We've had the 3661 for three years, always carry about 1/3 tank of water for toilet use while on the road. I drain and replace this water about every six to nine months. Question: how do I add cleaner to the water tank or do I need to worry about it? I'm taking a job where I will need to have and use my fresh water tank. Thanks.