Pump the tank out jet the leech lines as best you can get 4 gallons of SEPTIC DRAINER AND POUR RIGHT INTO THE DISTRIBUTION BOX. Then pour some bioclean after shock or rid x into the tank and wait and see what happens. Then add septic drainer and bio clean as recommended by the manufacturer. If you don't have a distribution box pour the septic drainer directly into the leech lines install a clean out if you can't access fro the tank. It may take a few weeks or month before you notice any changes.