Causes of Septic Problems: Leaks
About half of the septic failures I investigate are caused by leaking toilets. Sometimes the flapper valve (that lifts to flush the toilet) is leaking. That is evidenced by tiny streams of water trickling down the inside of the bowl. Replace the rubber flapper for about two dollars if there's any doubt.
Sometimes the valve that turns the water off when the toilet tank has refilled is defective or improperly adjusted. There is a "water level" line marked on the inside of the back of the tank. The valve should shut the water off by the time it reaches that line. If the water level rises just an inch or two above that line the water flows into a vertical overflow pipe (or over a little wall in the corner of the tank) and out to the septic system.
With either type of leak, if the water shut-off valve in the tank is a "ball-cock" valve (with a plastic float about the size of a softball attached to a metal rod) you are better off replacing it with a brand called "Fluidmaster". They are about eight dollars. The float rides up and down on a shaft, and the water is either fully on or fully off.
With the "Fluidmaster" valve the water level in the tank will keep dropping until the float has ridden down the shaft to a certain point. Then all of a sudden the water will turn on full force, alerting you that something's amiss with that toilet.
As stated in the last paragraph of the previous page, a septic system is made to accept only intermittent flows of water. Even a brand new septic system will quickly fail if it receives way too much water, twenty-four hours a day. It needs to soak down when fixtures are off, or you're sleeping, or away at work. A leak of twenty gallons an hour equals four hundred eighty gallons in twenty-four hours. (Your system is designed with expected water usage of 75 gallons per day per person with the possibility of two persons per bedroom. A 3 bedroom system is designed with an expected maximum flow rate of 450 gallons per day, as stated on the Tank Size page)
Recovery from a leak is not automatic, instantaneous, or guaranteed. Often the tank is overfilled for extended periods of time, defeating the baffle and allowing "suspended" solids to clog the fields, as well as interfering with the digestion process in the tank. When the leaching area has been flooded by a long-term leak, once it's fixed it must recover from its flooded condition and at the same time handle the normal needs of the household. Often it can't do both. I recommend that after all leaks are fixed the tank be pumped and water usage be minimized for a few days after the pumping (within reason). The idea is to maximize the amount of time it takes to refill the tank to the level where it starts to feed the leaching area. During this time the leaching area has a chance to recover from its flooded condition. When it starts to receive liquid from the tank again, and you've resumed normal water usage, it will hopefully be able to handle the usual daily flow.