Marlies

Fifteen years on a tank, and the bacteria packet question deserves a direct answer rather than a diplomatic one: a functioning tank is not short of bacteria. It receives a fresh supply several times a day from the thing it is designed to receive.

The situation where additives get discussed seriously is after something has genuinely wiped the tank out, which is rare and is not a monthly maintenance scenario.

The one that is missing from every list: know where your tank and drain field actually are, and do not park or build on the field. That will cost you more than every item on this list combined and nobody mentions it because it is not a product.

Ask the pumper is genuinely the best advice in this thread.