What goes down your drain end up in the septic tank. This can be a big problem if you are sending household grease and cooking fats down the kitchen sink because the bacteria that thrive in septic tanks don't eat solidified grease. The result of excessive grease in your septic tank is an obstruction of liquid entering and exiting the tank. The best way to remove grease from your septic tank is to never let it in there to begin with. But if you need to flush the grease out, there are a few ways to do it.
Pump your septic tank out. This is the most effective way to get everything out and start with an efficient septic system, free of unwanted grease and sludge. If you don't want to pump the entire unit out, skim the grease from the top of the tank and remove it.
Install a grease trap, otherwise known as a grease interceptor. This is a reservoir close to the area where the grease is coming from (such as the kitchen sink). In the reservoir, baffles collect water and allow the grease to rise to the top before the water is sent to the septic tank. Remove the grease collection unit from the trap at least twice a year to prevent it from clogging.
Pour 1 cup of a commercial acid-based drain cleaner down the kitchen sink. This will not unclog a serious problem but can serve as maintenance to keep grease levels under control.
Some states, such as Florida, have laws about any commercial product being advertised as a sewage degreaser. Be wary of commercial products claiming to clean your septic system of grease.