What not to put down a garbage disposal (a plumber's honest list).

The short list: grease, coffee grounds, eggshells, potato peels, celery, pasta, rice, and bones. None of it belongs in a garbage disposal, and most of it doesn't actually hurt the disposal. It hurts the drain line behind it, which is the part that costs real money. Here's the why behind each one.

We've been pulling apart kitchen drains in southeast Michigan since 1979, and the same handful of ingredients shows up in clog after clog. A disposal is a chopper, not a magician. Whatever goes in still has to travel 20 or 30 feet of drain pipe afterward, and that pipe has opinions.

The list, with the reasons

• Grease, oil, and fat. The worst offender. The disposal passes it through warm and liquid, then it cools in the line and coats the pipe walls like candle wax. Every pass adds a layer. Months later the line is half its diameter and everything else starts catching. Pour grease into a can, let it harden, trash it.
• Coffee grounds. They go through the unit fine, which is why people think they're safe. Then they settle in the P trap under the sink and pack into a dense, coffee scented sludge. Trash or compost, never the drain.
• Celery and other fibrous vegetables. Celery, corn husks, asparagus ends, onion skins. The strings don't chop, they wrap. They wind around the flywheel like thread on a spool until the unit jams. If yours is already humming and stuck, our humming disposal fix walks you through clearing it.
• Potato peels. Starch is the problem. Ground peels turn into a paste that sticks to everything it touches, and a sink full of them can stop a drain in one go.
• Pasta and rice. They keep swelling long after they go down. A small amount rinsed off a plate is fine. A pot's worth becomes an expanding plug in the trap.
• Eggshells. The shell grinds into gritty sand that settles in the line, and the membrane inside can wrap the impellers. Cheap to throw away, annoying to fish out.
• Bones. Small fragments might survive the trip, but bones are the classic flywheel jammer, and big ones can crack the grind components outright.

The cold water rule

Run cold water before you flip the switch, the whole time it runs, and for 15 seconds or so after. Cold, not hot. Cold water keeps any fat that snuck in solid enough for the disposal to chop and the drain to carry. Hot water melts it on the way down, and melted fat is exactly how the candle wax problem starts. The trailing water matters too, because it pushes the ground food all the way out of the trap instead of leaving it parked there.

The ice and salt trick

Once a month or so, fill the chamber with a couple cups of ice cubes and a good handful of coarse salt, run cold water, and let it grind until the ice is gone. The ice and salt scour buildup off the grind ring and flywheel, which is where most disposal odors live. It sounds violent. That's normal, and the unit is built for it. It's the cheapest maintenance in your whole kitchen.

Remember what the disposal feeds into

This is the part most lists skip. Your disposal empties into the same kitchen drain line that's been catching grease and grit since the house was built. The disposal almost never clogs itself. It just delivers material to a line that's already narrowing, and the clog forms somewhere past the trap where you can't reach it. That's why the question isn't "can the disposal grind this" but "do I want this in my drain line." A newer unit with a finer grind helps, and we cover when that swap makes sense in our repair or replace framework, but no disposal makes grease safe.

Thanksgiving is our busiest disposal week

Every November we get a run of calls from Novi kitchens the day after Thanksgiving. It's the busiest disposal week of the year, and the story is always the same: turkey fat down the drain, a bowl of potato peels behind it, and a houseful of guests when the sink backs up. If one sentence from this list sticks, make it this one: on the big cooking holidays, scrape into the trash and let the disposal handle the rinse water. Your Friday will go better.

Quick answers

Can grease go down a garbage disposal?

No. The disposal passes it through liquid, then it cools and coats the drain line until the line clogs. Pour it into a can, let it set, and put it in the trash.

Are coffee grounds bad for a garbage disposal?

Yes, but the damage happens past the unit. Grounds settle into a dense sludge in the P trap and slowly choke the drain. Trash or garden instead.

How do I clean a garbage disposal?

A couple cups of ice and a handful of coarse salt, ground up with cold water running, scours the unit clean. Monthly is plenty, and it handles most odors.

Countryside Plumbing is a licensed master plumber serving Milford, Novi, Farmington Hills, and southeast Michigan since 1979. Garbage disposal repair and replacement is everyday work for us. Free quotes at 248-705-7543, and we leave your house clean.