If you are sanitizing, then run your on-board water pump and pump the water in the tank through all the lines and drain from your holding tanks.
But, your low point drains do not drain your fresh water tank. The low point drains are designed to drain the water pipes, they won't drain the fresh water tank.
To drain the fresh water tank, you should have a valve sticking out of the tank under the camper with a valve on it. It drains the tank, not the water lines. Look for that valve under the camper wherever the water tank is located.
But if you want the entire system truly sanitized, then pump all that water through your lines.