How long should you run the water through the kitchen disposer before you can be reasonably assured that all the stuff has been washed out of the plumbing?

Having worked in chemistry and dealing with water systems, I would say it depends on what you put down there, how much went down, how finely it was chopped, the flow rate of the water you are using and how far it has to go to hit the main line. A good rule of thumb is three line volumes, but that might be unreasonable. And if you are trying to wash away something that has a lot of grease, you might want to run hot water for a few minutes before you pour the greasy stuff down. It helps pre-heat the line. When liquid grease hits a cold pipe, it solidifies really quickly.

I never thought of that. Thanks for the good information.

The booklet that came with my first disposal years ago said 12 seconds. I have a new Waste King disposal and the owner booklet says 15 seconds. I let my cold water run probably twice that. And only use cold water in a disposal. I mention that because I know someone who, well, who had an expensive experience. No, it wasn’t me.

It’s better to try never put grease down the drain. Sooner or later it will clog a pipe, either on your property or in the main sewer. It’s a real mess to remove, time consuming and costs a lot. Either way, you’ll pay for it in your bill on in your taxes.

An inexpensive disposer can’t handle much. When we rented, they always seemed to install super cheap disposers. They can’t handle much food waste, and you’d best not try putting bones down them. The bigger more expensive disposers are much better at grinding up food and bones.

My father studied our kitchen disposer pretty thoroughly. He discovered that if you have a lot of debris of the same type (such as potato peelings), it’s best to roll it up in newspaper and throw it away. It would clog the line. He insisted that it was important to vary what we put down it.

Edit: he also insisted we run cold water hard, for at least 15 seconds after the disposer had emptied.

Hmmm. I’ve always just run it until it sounds clear.
I don’t ever pour grease down the drain, either.

Potato peelings are the devil! You can not run potato peelings through the disposal. I don’t think it’s because they’re the same things. I think it’s the starch. I think it coats everything and makes it so slimy that the blades can’t cut through it.