Parts of a Septic Tank

How this list was compiled: Part names and every detail line were checked, for facts only and with nothing copied, against pages read on 2026-09-20. The United States Environmental Protection Agency: https://www.epa.gov/septic/how-septic-systems-work (the septic tank is a buried, watertight container usually of concrete, fiberglass or polyethylene; solids settle as sludge, oil and grease float as scum; compartments and a T-shaped outlet keep sludge and scum from leaving; the liquid wastewater, called effluent, exits to the drainfield; the drainfield is a shallow covered excavation in unsaturated soil; the soil removes harmful coliform bacteria, viruses and nutrients as the wastewater percolates); https://www.epa.gov/sites/default/files/2015-06/documents/septicsmart_longhomeownerguide_english508_0.pdf (the homeowner guide: lids and manhole covers; the T-shaped outlet; a tank needs pumping when the bottom of the scum layer is within six inches of the bottom of the outlet or the top of the sludge layer is within 12 inches of the outlet; inspection at least every three years and pumping every three to five years); https://www.epa.gov/septic/frequent-questions-septic-systems (the access riser seen as a black or green disc; the effluent filter; the distribution box checked to see that the drain lines receive equal flow); https://www.epa.gov/septic/types-septic-systems (the conventional system: effluent piped to a shallow underground trench of stone or gravel). Extension services: https://extension.psu.edu/septic-tank-pumping (a single-chamber or dual-chamber tank; the first chamber; sludge and scum layers; the exit filter; two large central access ports, called manholes; risers from the access ports to the soil surface; the absorption area and its biomat); https://content.ces.ncsu.edu/septic-systems-and-their-maintenance (the tank, the drainfield and the soil as the three parts of a system; a two-compartment tank; the outlet baffle or sanitary tee, which keeps solids from flowing out with the liquid; the effluent filter fitted in place of the sanitary tee in the second compartment; a watertight riser over the tank; perforated pipe in gravel-filled trenches; the biomat that forms in the soil just below the trench bottom); https://fieldreport.caes.uga.edu/publications/B1421/ (new tanks with two chambers and older tanks with one; the lid or access port, sometimes on a riser; the tee that lets out water from the middle layer only; the distribution box that sends wastewater to several lines; perforated drain lines over a layer of gravel); https://ohioline.osu.edu/factsheet/aex-740 (baffles, filters and the tank lid); https://septic.umn.edu/all-about-septics (light solids float to form a scum layer and heavy solids sink to form sludge; inlet and outlet baffles hold floating solids in the tank; inspection pipes let the tank be checked and the manhole is for cleaning; distribution boxes among the gravity distribution devices). Wikipedia: https://en.wikipedia.org/wiki/Septic_tank (T-shaped pipes at the inlet and the outlet that let liquid enter and leave without disturbing the crust; two chambers, each with an access opening and cover, separated by a dividing wall with openings about midway between the floor and the roof; wastewater enters the first chamber, where solids settle and scum floats, and further settlement takes place in the second) and https://en.wikipedia.org/wiki/Septic_drain_field (trenches holding perforated pipes and gravel, covered with soil; the biomat). Licence: own work

The drawing: Drawn for this site on 2026-09-26: a two-compartment concrete septic tank in section, the whole system in plan, and one drainfield trench cut across. Our own geometry; nothing traced or copied; the text sources are listed in this dataset's source. Licence: own work