The average 2 bedroom home will use approximately 200 gallons of water daily in baths, showers, washing clothes, dishes, flushing toilets and not to mention the countless other times the water is turned on and off. All of this use will fill up your tank quickly. The important part of your septic tank is to retain solids and re-transfer liquids to the drainfield. If you increase the number of people or waste going to the tank by as little as 25% for an extended period of time, it can overburden the tank and drainfield. Also faulty plumbing fixtures, such as a running toilet can force hundreds of gallons of water through the tank and into the drainfield. If this occurs this can cause an oversaturation of the earth under the drainfield and failure of the system.