Septic Tank Pumping, Drainfield Care, and Warning Signs

The tank separates; the drainfield treats.

EPA describes the septic tank as a buried, watertight tank that receives household wastewater. Heavy solids settle to the bottom as sludge, while grease and lighter solids float to the top as scum. The solids stay in the tank and the liquid flows to the drainfield, a shallow network of trenches or beds in the soil that removes contaminants.

The tank’s outlet is T-shaped to keep sludge and scum from leaving. When the tank fills with solids, they escape into the drainfield — and a clogged drainfield is the expensive part to replace.

EPA’s general guidance, and what changes it.

EPA says an average household system should be inspected by a septic professional at least every three years, and that household tanks are typically pumped every three to five years. Alternative systems with float switches, pumps, or other mechanical parts should generally be inspected once a year.

The factors EPA lists for your own schedule are household size, total wastewater generated, the volume of solids, and tank size. EPA also gives the measured trigger: pump when the bottom of the scum layer is within six inches of the outlet, when the top of the sludge is within 12 inches of it, or when sludge and scum together fill more than 25% of the liquid depth. Ask the service provider to record those levels at every visit.

Everything flushed or rinsed ends up in the tank.

EPA’s rule of thumb is to flush nothing but human waste and toilet paper. Wipes, grease, and chemicals disrupt the tank or pass through to the field. EPA also recommends limiting or eliminating a garbage disposal, which sends fats, grease, and solids into the tank that can clog the drainfield.

Water volume matters as well. EPA notes that toilets account for 25 to 30 percent of household water use, that older toilets use 3.5 to 5 gallons a flush against 1.6 gallons or less for high-efficiency models, and that spreading laundry across the week keeps the system from being flooded in one day. A running toilet can push a steady stream through the tank around the clock.

The field is soil, and soil can be crushed, invaded, and drowned.

• Parking: do not park or drive on it.
• Planting: keep trees far enough away that roots cannot reach the system; a septic professional can advise on the distance for your site.
• Placing: keep roof drains, sump pumps, and other rainwater drainage away, because excess water slows or stops treatment.

EPA lists the symptoms that call for a septic professional now, not at the next scheduled visit.

• Water or sewage from toilets, drains, and sinks backing up into the house
• Bathtubs, showers, and sinks draining very slowly
• Gurgling sounds in the plumbing
• Standing water or damp spots near or over the tank or drainfield
• Sewage odors around the tank or drainfield
• Bright green, spongy grass over the tank or drainfield, even in dry weather

Not every smell means failure: EPA notes an odor can come from a roof vent that lets the system equalize pressure, which is normal, though a blocked vent needs clearing. EPA also does not recommend septic tank additives. Leave opening the tank to a septic professional.