Checklist

How they work

Waste-disposal units have impellers (usually with metal bars) that rotate at high speed inside a grinding chamber, bashing and mashing the scraps down to a fine paste that's flushed away with water.

Some units have sliding impellers that are said to reduce the number of jams from food like chicken bones or corn cobs. But the models in our test that had sliding impellers all came with a special wrench to free jams!

What about the environment?

After you've ground up your food scraps and flushed them - what happens?

For city dwellers who can't make use of a pig, compost heap, or worm farm, waste-disposal units may have a place. But they do add to the burden on sewage systems, and also use quite a bit of water while running. In our test we used 15 litres of water for every 1kg of food.

Septic tank owners certainly shouldn't use waste-disposal units, because the tank will need more regular emptying - and can become overloaded.

Which is the best unit for your household?

If you have a large family, or are likely to use a disposal unit very often, go for a heavy-duty model. The grinder blade material is also important. Lightly galvanised steel will wear out far quicker than stainless steel.

Dos and don'ts

These units will munch up kitchen scraps as long as they're not too stringy or too hard.

It's best to avoid heavy bones like sheep shanks or stringy stuff like corn husks: these types of impossible-to-digest scraps may cause jams or bung up the machine.

Never put grease, fat, or oil down any waste-disposal unit or drain, as they can congeal and block the pipes.

Jamming

This is one of the biggest problems with waste disposal units and is often caused by trying to get rid of too much at once, especially if the waste is coarse. Models with sliding blades are claimed to reduce the likelihood of jams.

But note that you can't put just anything down your unit and expect it not to jam. Most manufacturers recommend you don't try and grind up large bones.

If you do get a jam or lose a teaspoon down the hole, unplug the unit under the sink before putting your hand in to clear it. Some models have a special tool for rotating the rotor to clear a jam.

Some units (with an induction motor) turn in the opposite direction each time you switch it on. This can reduce the chances of jamming. It also evens out the wear, because both sides of the grinder blades get used.

Drain blockage

The worst thing that can happen is drain blockage. If you get this problem, it's possible the unit is not grinding waste finely enough.

Noise

All waste disposers are noisy.

"Sound deadening" is available on more expensive models - but because most of the noise escapes through the plug hole, this sound deadening has minimal effect.

Installation

If you are a reasonably confident DIYer you can install a waste disposer yourself providing your sink has the special large hole required. Only a few simple connections into the sink waste are needed. But you will need to get an electrician to install a power outlet under the sink with a switch on the wall above.

Guards

Waste disposers have a rubber guard inserted in the entrance to the grinding chamber. This prevents splash back when operating the unit and helps stop unwanted objects going down the hole. Some guards are removable which makes cleaning and un-jamming the unit easier.

A word about price

When buying a waste disposal unit, shop around! There can be huge price differences for the same model among stores.