What You Should Never Put Down Your Garbage Disposal

Start with starch. Rice, pasta, bread, oatmeal and potato peels keep absorbing water after they go down the drain, and ground into a paste they swell into a thick sludge that settles in the trap and the first few feet of pipe. In a lot of island kitchens, leftover rice is the single most common thing scraped into the sink, and it is also one of the most common reasons a kitchen drain stops draining. Scrape the pot into the bin, not the sink.

Fibrous produce is the next problem. Corn husks, celery, onion skins, artichoke leaves, banana peels, pineapple tops and cores, mango skins and lu'au or taro leaves all have long, stringy fibers that wrap around the disposal's impellers instead of grinding. They either jam the unit outright or pass through as a tangled mat that catches everything behind it.

Hard items don't belong either. Mango seeds, avocado pits, peach stones, coconut shell, kalbi and chicken bones, and shellfish shells from a shrimp boil can stall the motor, dull the grinding ring or crack the chamber. A few small, soft bones won't ruin a good disposal, but a habit of feeding it bones will shorten its life considerably.

Grease is the worst offender because it doesn't look like a problem when it goes down. Bacon fat, oil from the fryer and the drippings from a pan of kalua pork pour as a liquid, then cool and harden on the inside of the pipe. Each time it happens, another layer builds up and catches rice, grounds and food particles. Running hot water only moves the grease a little further down the line before it sets. Let it cool in a can or jar and throw it out.

Coffee grounds and eggshells are the two items most people think are good for a disposal. They aren't. Grounds don't dissolve; they settle out of the water and pack into the trap like wet sand. Crushed eggshell does the same thing, and the thin membrane inside the shell can wrap around the impellers. Put both in the trash or the compost.

Then there's everything that isn't food at all: paper towels, napkins, twist ties, produce stickers, cigarette butts, "flushable" wipes and harsh chemical drain openers. Chemical cleaners in particular can damage the disposal's seals and the pipe itself, which is why we recommend the methods in our guide to preventing clogged drains without harsh chemicals instead.

It's worth knowing that older homes in Kaimuki, Kalihi, Manoa and Pearl City often still have original cast-iron or galvanized drain piping. Decades of scale and corrosion narrow the inside of those pipes, so grease and starch catch far sooner than they would in a newer PVC line. If your house is older, being careful with the disposal matters even more.

A large share of O'ahu homes, particularly on the North Shore, in Waimanalo and in parts of the Leeward and Windward coasts, are not on city sewer. They drain to a septic tank or a cesspool. Everything your disposal grinds ends up in that tank, and food waste breaks down much more slowly than household wastewater, so it adds directly to the sludge layer at the bottom.

The result is that heavy disposal use can noticeably shorten the time between pump-outs, as we cover in our guide on how often to pump a septic tank in Hawai'i. Grease is especially hard on these systems because it floats into the scum layer and can travel out into the drainfield, where it clogs the soil that's supposed to absorb water. The U.S. EPA's SepticSmart guidance makes the same point: limit what goes down the disposal if you're on a septic system.

If you're on septic and want to keep using a disposal, use it lightly, scrape plates into the bin first, and keep grease out entirely. If you aren't sure what your home is connected to, our septic system services team can tell you and check the condition of the tank while we're there.

Some disposal problems are simple. If the unit hums but won't spin, it's usually jammed; turn off the power, and use the hex wrench that fits the socket on the bottom of the unit to work the impellers loose. If it won't do anything at all, press the red reset button on the underside. Never put your hand inside the chamber, even with the switch off.

Other problems point past the disposal itself. Water that backs up into the other side of a double sink, slow drainage that keeps coming back, gurgling from the drain, or a bad smell that returns no matter how often you clean the unit usually means the clog is in the line, not the machine. That calls for clogged drain service to clear the pipe properly rather than another round of plunging.

Water dripping from the bottom of the unit usually means an internal seal has failed, and a leak at the top usually points to the sink flange. Most disposals last roughly eight to twelve years. If yours is leaking from the body, rusted, or jamming every few weeks, replacement is often the better value, and our garbage disposal repair and installation service can tell you which makes sense.

Run cold water before, during and for about fifteen seconds after grinding. Cold water keeps any small amount of fat solid so it gets chopped and carried away instead of coating the chamber. Feed scraps in gradually rather than all at once, and let the unit finish before you turn it off.

Use it regularly, even briefly, so the parts don't corrode or seize, which happens faster in Hawai'i's humid, salty air. To freshen it, grind a handful of ice cubes and a few small citrus peels. Treat the disposal as a way to handle the small bits that fall off a rinsed plate, not as a replacement for the trash can.

If your disposal is jammed, leaking, or your kitchen sink keeps backing up, call Alpha Omega Plumbing at (808) 847-5414. We've served homes across O'ahu since 2014, from Kailua to Kapolei, and we'll tell you honestly whether you need a repair, a new unit, or just a clear drain line.