Garbage Disposals: What Not to Put In One

What should you never put in a garbage disposal?

Grease and oil, fibrous foods such as celery, corn husks and artichokes, large starchy loads such as rice, large bones, and anything that is not food — that is the manufacturer’s own list [1]. Coffee grounds are on the EPA’s list of things to keep out of the drain in a septic home [2].

Grease and oil. Liquid in the pan, solid in the pipe. The manufacturer’s guidance puts “grease and oils that solidify” on the avoid list, and the EPA says never to pour cooking oil or grease down a drain [1][2]. It coats the inside of the line, catches everything else that passes, and is often the reason a blockage shows up somewhere nowhere near the sink.

Fibrous foods — celery, corn husks, artichokes are the manufacturer’s own examples [1]. The fibres wrap around the grinding parts and travel as a mat that catches at the first change of direction in the pipe.

Large starchy loads — a lot of rice or potato peels at once [1]. A small amount goes through; a pot’s worth is a plug.

Coffee grounds. The EPA lists coffee grounds among the things not to send down the drain on a septic system [2]. In our experience they also settle in the trap and the horizontal run on a sewer connection, building a silt bed.

Large bones and non-food items — plastic, glass, metal, paper [1]. They do not grind; they ride around inside and wear or jam the machine.

• Cold water, not hot — cold keeps fats solid so they grind and travel instead of coating the pipe [1]
• A moderate-to-strong cold flow before and during grinding, and keep the water running for up to 15 seconds after switching off [1]
• Cut large scraps smaller and feed a little at a time rather than packing the chamber [1]
• Grease into a container to harden, then into the bin — not into the sink [2]

Can you use a garbage disposal with a septic tank?

You can, but the EPA’s advice is to limit it or not use one at all [2].

Everything that goes down a kitchen drain on a septic property ends up in the tank. The EPA’s guidance is direct: eliminate or limit the use of a garbage disposal, because doing so significantly reduces the fats, grease and solids that enter the tank and could clog the drainfield [2].

The EPA also lists the volume of solids in the wastewater among the factors that decide how often a tank needs pumping [2]. So if you do use a disposal on septic, expect the tank to need attention sooner, and keep grease out of it entirely.

Why is my garbage disposal humming but not working?

It hums but does not turn. Something is jammed. Switch it off at the wall, then use the hex key that came with the unit in the socket underneath to work the motor back and forth until it turns freely. Never put a hand into the chamber, even with the switch off.

It does nothing at all. Press the reset button on the underside of the unit; the motor’s thermal overload trips after a jam or a long run. If it trips again straight away, stop — that is a fault, not a habit.

It leaks. Look at where: the sink flange above, the dishwasher inlet, the discharge elbow gasket, or the body itself. A leak from the body usually means a new disposal; the others are parts.

Why won’t the dishwasher drain after a new disposal is installed?

Usually because the knockout plug inside the disposal’s dishwasher inlet was never removed.

Two things go wrong with the dishwasher side of a disposal. First, on a new unit the knockout plug inside the dishwasher inlet has to be driven out and removed — if it is left in place, the dishwasher cannot drain; if it is driven in and not fished out, it rattles around inside the chamber.

Second, the dishwasher drain hose needs a high loop or an air gap so that dirty water from the sink cannot run back into the machine. On our installations that loop is fastened up under the counter, not left lying in the cabinet.

What this means in Tampa Bay

Many older houses here drain the kitchen through galvanized or cast-iron branch lines that have narrowed inside over the decades. On those, the disposal is rarely the problem — it is the last machine in front of a pipe that has been getting smaller for years.

If a kitchen line blocks more than once a year, the useful next step is a camera down the line rather than another chemical or another disposal. We install disposals, we replace the trap and tailpiece arrangement when it is the cause, and we look at the line when it is not.

FAQ

Sources

We review and cite. We do not reproduce a paper or a manual — follow the links for the originals.

1. [1]Operating a Continuous-Feed Waste Disposer — Whirlpool Corporation (product help; Whirlpool owns the InSinkErator brand) · 2026Manufacturer's manual · cold water while grinding and why; up to 15 s of cold water after switch-off; items to avoid; ice and citrus cleaning
2. [2]How to Care for Your Septic System — US Environmental Protection AgencyGovernment or standards body · eliminate or limit garbage disposal use on septic; never pour grease down the drain; coffee grounds; volume of solids as a pumping factor