Aerobic Septic System Dos and Don'ts: What Can Go Down the Drain

Aerobic septic dos and don'ts at a glance

An aerobic system is a small wastewater treatment plant in your yard. It runs on live bacteria, air from a compressor, and a steady, moderate flow of ordinary household wastewater. Almost every rule below protects one of those three things.

Here's the short list. The sections after it explain the ones people ask about most.

What can go down the drain on an aerobic system?

Human waste, toilet paper, and ordinary wash water from sinks, showers, dishwashers, and laundry. That's what the system is designed for. Everything else either doesn't break down, slows the bacteria, or has to be pumped out later at your expense.

Texas A&M AgriLife's homeowner guide for aerobic systems is specific about the problem items. 'Septic safe' on a package, AgriLife notes, usually means the product will flow through the pipes, not that it breaks down. Those items still collect in the tanks and add to maintenance.

• Wipes of any kind, including ones labeled flushable or septic safe.
• Paper towels, rags, diapers, feminine products, condoms, and dental floss.
• Cat litter and coffee grounds, which add straight to the sludge that has to be pumped.
• Cooking grease, fats, and oils. Heavy bath and body oils also raise the grease load.
• Toxic drain cleaners, paint, solvents, and garage chemicals.
• Unused medicines. AgriLife calls antibiotics and prescription drugs extremely hard on the system's microbes.
• Automatic toilet-tank and shower cleaners that drip chemicals into the system all day.
• Lotion-treated toilet paper in large amounts, which floats and builds up a scum layer.

Can you use bleach with an aerobic septic system?

Yes, in normal household amounts. Ordinary laundry use and a bleach-based bathroom cleaner now and then aren't what wrecks an aerobic unit. AgriLife's advice is simply not to overuse it, because bleach additives affect the biology of the tank and everything downstream.

What hurts is volume and habit: bleach in every load, daily bleach-tablet toilet cleaners, or pouring a gallon down the drain to 'clean the system.' Antibacterial soaps work the same way over time.

Don't confuse household bleach with the system's disinfection. A tablet chlorinator takes calcium hypochlorite tablets labeled for wastewater, not bleach and not pool tablets. Some systems use a liquid chlorinator instead, which is designed for liquid chlorine; ask your provider what yours takes. Our aerobic chlorine tablet guide covers what to buy.^source

Can you have a garbage disposal on an aerobic system?

You can, but it costs you. AgriLife lists four ways a disposal loads an aerobic system: more solids go in, the food isn't pre-digested so it takes longer to break down, you run extra water to rinse it through, and the smaller particles take longer to settle. Homes that use a disposal need a larger system and more maintenance.

If your home already has one, use it lightly. Scrape plates into the trash, keep grease, peels, and coffee grounds out, and expect your provider to flag rising sludge sooner. If you're building, tell your designer you plan to use a disposal so it's accounted for.

How much laundry can an aerobic system handle in a day?

Less than you'd think in a short window, and plenty if you spread it out. AgriLife notes that many residential aerobic units are rated around 500 gallons a day but only treat about 60 gallons an hour, while a normal washer uses 30 to 40 gallons per load.

Here's the math on a laundry marathon. Four loads back to back over about three hours is 120 to 160 gallons, which is at or over what a 60-gallon-an-hour unit is built to take in that time, and that's before anyone showers or runs the dishwasher. Water that arrives faster than the unit can treat it gets pushed through with less time in the aeration chamber.

The fix is easy: one or two loads a day instead of all of them on Saturday, and full loads instead of small ones. Your unit's rated capacity should be on the permit or the control panel label. If your family truly needs heavy laundry days, ask your provider or installer about a flow equalization tank, which holds wastewater and feeds it to the unit at a pace it can handle.^source

Water softener backwash and aerobic systems

Texas has a specific law on this. Under Health and Safety Code 366.013, a water softener may discharge into a septic system only if it conserves water by design, regenerates with a demand-initiated regeneration (DIR) control, and has a label on the outside saying so. Older softeners installed before September 1, 2003 can stay until they're replaced or the septic system is replaced.

For aerobic systems there's an extra condition. The same section says it doesn't apply to aerobic, nonstandard, or proprietary systems unless the softener drain line bypasses the treatment unit and flows into the pump tank or directly to the disposal method. AgriLife's guidance points the same way: automatic backflushing adds water the system doesn't need, and chemicals from some water conditioners may need to be plumbed around the treatment tanks to the pump tank.

In plain terms, don't assume softener brine should run through your aerobic unit. Ask your maintenance provider where your softener drain goes. If it's tied into the house drains ahead of the treatment unit, ask a licensed installer what it takes to reroute it, and whether any change needs county approval. Point-of-use reverse osmosis units, like the one under a kitchen sink, are allowed to discharge into a septic system under the same law.^source

Keep clear water out of the system

Clean water is still water, and an aerobic system has a daily and hourly limit. AgriLife lists several sources that use up capacity for nothing.

• Air conditioner condensate. It isn't sewage; route it around the system.
• Gutters and yard drainage. Keep downspouts and runoff away from tank lids and the spray area.
• Indoor whirlpool tubs and multi-head showers, which can dump more water at once than the unit's hourly rate.
• Ice machines and other appliances that drain clear water all day.
• Rainwater leaking into tanks. Look for low spots over the tanks where water pools, and loose riser lids. If the spray heads run during a rain, mention it to your provider.

Power, the aerator, and the alarm

The aerator (air compressor) has to run all the time. AgriLife is plain about it: aerobic systems must have a continuous supply of oxygen to keep the microbes healthy. Turning the breaker off to quiet the hum, or unplugging it while you're away, lets the system go septic, and it starts to smell.

Running it costs less than people fear. This site's planning range is $120-$240 a year in electricity; our guide to aerobic system electricity use shows the math. If the aerator goes quiet on its own, that's a repair call, not a reset; see aerobic air pump failure symptoms.

When the alarm sounds, cut back on water right away and call your provider. The alarm usually means the pump tank is high. On timer-controlled spray systems, which is every spray system in Kaufman County, Texas rules only require a reserve of about a third of a day's flow between the alarm level and the tank inlet, so a normal day of laundry and showers can fill it. During a power outage, the same logic applies: go easy on water until power is back. More in our guide to what a septic alarm means.

Spray area dos and don'ts

The spray area is part of the septic system, even if it looks like lawn. Texas rules require it to stay planted, bar food crops, and keep anything within 10 feet of a sprinkler that would block even coverage out of it. In Kaufman County the heads are purple pop-ups that spray between midnight and 5am.

• Do keep grass or other plant cover growing. Bare ground isn't allowed, and grass uses the water and nutrients.
• Do water in a dry summer if the grass needs it. Spray areas are sized for the wettest season, so they run short in August.
• Don't plant vegetables, fruit trees, or herbs in the spray area.
• Don't put a shed, playset, trampoline, raised bed, or parked trailer within 10 feet of a head.
• Don't let kids or pets play in the spray area while it's wet. AgriLife says residents and pets should avoid contact with the effluent.
• Don't move, cap, replace, or add spray heads yourself. Kaufman County requires a TCEQ license for any sprinkler repair. Our aerobic sprinkler head guide covers what you can do.^source

Guests, holidays, and coming home from vacation

Houseguests mean more showers, more laundry, and more dishes, all at once. You don't have to ration anyone, but it helps to spread the laundry, avoid back-to-back long showers, and keep the grease out of the sink during holiday cooking.

Long trips cause the opposite problem. With no wastewater coming in, the bacteria population drops. AgriLife's advice is to ease back in over the first couple of days home and avoid heavy water use, such as a pile of vacation laundry, until the system recovers.

Chlorine tablets and safety around the equipment

Keep the chlorinator stocked with the right tablets, or confirm your provider does. Texas rules require calcium hypochlorite labeled for wastewater disinfection, and TCEQ warns against pool tablets. AgriLife adds a storage rule: chlorine tablets release chlorine gas, so don't store them in the house, the garage, or anywhere near metal tools.^source

Keep lids closed and secured. AgriLife recommends heavy lids, safety screws, or locks on risers and control panels where kids and pets play.

The rules that are different in Kaufman County

Some advice you'll read online doesn't apply here. Texas lets homeowners maintain their own aerobic systems after the initial two-year service policy. Kaufman County's TCEQ-approved order doesn't: every aerobic system must have a maintenance contract, all maintenance must be done by a licensed maintenance provider, and inspections happen every four months.^source

So the most important 'do' is paperwork. Keep your contract current, make sure the renewal reaches the county at least 30 days before it expires, and keep your reports. If you need a provider or want to compare prices, start with our aerobic septic maintenance page for Kaufman County.^source