Septic-Scrub works best when the field is not saturated and the water level is down to the stone soil interface. This is the same as preventative maintenance. A presurized system is more difficult to treat. I do not like putting Septic-Scrub into the pump tank because of some reaction with material in the tank and the loss of product due to the addition of water in the tank to activate the pump. You can never pump all of the product over. A better way if possible would be to clean the system out as you are contemplating. Install a cut-off valve in the line leading to the pump tank so that water cannot flow back into the tank. Dissolve the Septic-Scrub in water, use something such as a garbage can, and then pump the solution through one of the risers into the system. This gets 100% of the product into the system. If you have questions, please do not hesitate to call.