If you add that to the tank, it may break down the sludge in the tank as advertised but the sludge will particulate into small pieces and clog up your pipes in the leech field. This obviously creates an even worse problem. My advice, pump the tank once every two years depending upon size of the tank and how many in the household.
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That happened to us. The prior owners used it once a month and now we have to have a new drain field dug.
May I ask how much that cost you?, sounds $$$