The OP put "empty the tank" before "achieve a PH in the tank".
Rinsing with water doesn't look hopeless to me, if done several times after emptying every time.
Reaching all the parts with water reduce the number of rinsing steps. A watering can maybe? Beware of heat the first time, and of spat every time. DI water is useful only the last time.
Then, what to do with the removed NaOH is an interesting question, if not neutralized.