A Septic Tank is where wastewater flows to, from the house. The tank is designed to retain waste water and allow heavy solids to settle to the bottom. These solids are partially decomposed by bacteria to form sludge. Grease and light particles float, forming a layer of scum on top of the waste water. Baffles installed at the inlet and outlet of the tank help prevent scum and solids from escaping. A properly functioning septic tank will release water, which has been separated from scum and sludge, to the leach field and will break down biodegradable products. A properly maintained septic tank will not contain non-biodegradable materials; the sludge, scum and oil depths would be less than 1/3 of the liquid depth of the tank; the inlet and outlet baffles will be in place and appropriately sized; and the filter, if applicable, will be relatively clean and unobstructed.
A Leach field is a solid pipe that leads from the septic tank to the leach field, where the wastewater is channeled into one or more perforated pipes set in trenches or beds of gravel or a perforated concrete structure. Unlike the septic tank, the bacteria in the leach field require air to survive. Here the water slowly seeps into the underlying soil. Dissolved wastes and bacteria in the water are trapped or adsorbed to soil particles or decomposed by microorganisms. This process removes disease-causing organisms, organic matter, and most nutrients (except nitrogen and some salts). The treated wastewater then either moves to the ground water or evaporates from the soil.
Back in the day, the rule of thumb was if you have a dry well, then you would never have to pump your tank. In this day in age, that rule no longer applies. Dry wells are not used anymore, because the new style systems are designed for leach fields to leach a lot cleaner. The dry well was used for the soaps, detergents and chemicals from your home, now the chemicals are run through the tank, the soaps kill the bacteria that is needed to level the tank, with that bacteria being killed is causes rot and sends it to the leach field.
Distribution Box (D-Box)
Most, but not all, systems have a d-box. Once the effluent is separated in the septic tank, the distribution box, located in the leach field, dispenses the effluent into the leach field. The distribution box should be laid level with the existing pipes dispersing the effluent evenly into the lateral pipes with very little to no sludge content. Riser: A riser is a green hard-plastic ring and cover that is installed on the tanks access covers. They allow for easy access to the tank so that the covers will not need to be dug.