Waste, or garbage disposal units have been common in the US for many years now, and are slowly finding their way into European kitchens. These are usually fitted directly under the kitchen sink and catch solid waste (such as vegetable peelings) before it gets into the drain. When switched on, the waste disposal unit grinds food materials into a runny pulp, which is then washed down the drain without causing a blockage.

In order to accommodate the pieces of solid waste, the drainage hole for a waste disposal unit is much bigger than the usual plughole found in sinks and washbasins, so if you want to install one in your own kitchen you will probably need a new sink.

As with any machine, proper use, care, and maintenance will extend the life of your waste disposal. It will also help to avoid the unpleasant business of trying to unblock it yourself, and will cut down the chances of having to call in a plumber¹ because your drains are full of the remains of last night's dinner.

How to use a waste disposal unit

The importance of water

Before switching on a waste disposal, run the cold tap for a few seconds to ensure a good flow of water through the unit. Water acts as both a lubricant and a coolant while the unit is operating, which is why you should use cold water for grinding. Hot water may cause it to overheat and trip the cutoff switch which most disposals are fitted with.

During the grinding process a good flow of water keeps the resulting pulp thin and runny, making it easy to flush away.

When grinding has finished, switch off the unit but keep the water running for a further 5 - 10 seconds to make sure all the pulp has been washed down the drain.

How long to grind

The unit should already be running at full speed before you put anything into it. Once the process has begun you should continue running the unit until you hear no more sounds of the food being ground.

The motors which power these units, although quite powerful, are designed to be used for short periods - usually no more than a minute at a time, and they can easily be damaged if run for too long, run without water, or forced to grind too much at once.

Don't stuff everything into the unit at once - feed it in gradually. If you have a lot of material to get rid of, bear in mind the time limits mentioned above and grind it in stages, allowing the unit to rest for a couple of minutes between each usage.

What to grind and what not to grind

Almost any soft food material is safe - vegetable peelings, apple cores, rice, tea leaves, cooked meat, pastry, bread, nuts, pickles, porridge - all will pass through safely as long as the water is running. Grinding citrus skins will help to reduce foul odours which sometimes come from waste disposals as scraps of rotting food accumulate inside the unit.

Harder materials can also be ground - in fact it's beneficial to the unit to grind things like chicken bones, ice cubes, eggshells, and small fruit pips and stones. These scour the workings of the unit and help to remove the coating of gunk and grease which builds up with use. Vinegar ice cubes will have a two-fold effect because of the acid in the vinegar.

It's not recommended that you attempt to grind pips as large as an avocado stone - anything up to the size of a hazelnut (filbert) should be fine for household units, and any bones larger than a chicken thigh should be chopped up.

As a general rule, it's best to avoid putting anything other than food into a waste disposal, although paper towel shouldn't give it any problems. Allowing any kind of plastic food wrapping to get into it is asking for trouble.

Do not try to grind fibrous materials such as corn husks, artichokes, asparagus, even celery. These can seize up your waste disposal and block your drain. Coconut shell is also best avoided - partly because of the coconut hairs, and partly because it is just a little too hard for all but industrial waste disposals, and bits of shell can even be spit back out of the unit.

Uncooked meat, especially gristle and connective tissue, can be tough enough to wrap itself around the innards of a waste disposal unit, and once stuck there it will begin to decompose, filling your kitchen with the stink of rotting meat.

Don't pour fat or grease into the disposal². It's unlikely that it will cause any harm to the unit, but fats which are solid at room temperature will inevitably block your drain and the waste disposal. Pour them into a jar which is kept in the fridge until full, then throw it away like any other piece of rubbish.

Care and maintenance tips

Apart from what has already been mentioned - grinding citrus skins to reduce odours, and small bones to scour the inside of the unit, there are a few other points to remember when looking after your waste disposal.

• Don't pour undiluted bleach or caustic cleaners into it.
• If smells from the drain become bad, buy a proprietory waste disposal cleaner or de-greaser.
• A cup of baking soda in half a sinkful of cold water will also help to reduce smells.
• If you have a dishwasher which drains through the waste disposal, either run the unit before you switch on the dishwasher³, or better yet run it as the dishwasher is draining, which will get plenty of soapy water through the unit and give it a good clean. Make sure you rinse it thoroughly with clean water afterwards though - some soap ingredients can be corrosive to components inside the unit.

Troubleshooting

A couple of important safety tips

• Before doing any work on the unit, isolate it either by removing the fuse/breaker, or by unhooking the power cables.
• NEVER put your hand into a waste disposal unit unless you've already isolated it yourself.

The unit doesn't start when switched on

• Check the reset button - usually red and usually on the bottom of the unit. Push it in and try the unit again.
• Check the fuse.
• Check the connections at the motor and at the on/off switch.

If all the electrics seem ok, you may have a burnt-out motor.

The waste disposal makes an unusually loud, or a metallic noise

• Look for a metallic object in the unit.
• Check that the mounting screws/bolts are tight.
• Something may have come loose inside the unit.

The unit hums when switched on but doesn't turn

Switch it off immediately - your waste disposal is jammed. Waste disposals come supplied with an Allen key which fits into a hexagonal hole at the base of the unit⁴.

Isolate the unit. Insert the key into the hole at the bottom of the unit and work the key backwards and forwards until it turns freely in full circles. You may be able to see what was causing the jam through the drainage hole in the sink - remove it with a pair of tongs or pliers if you can reach it. If it's too far in to reach, you will have to take the waste disposal out of the line, turn it upside down and shake the object out.

If it only turns a little or won't turn at all, you will either have to remove and dismantle the unit or call in a professional. There may be something hard like a piece of metal or a small stone in there, or the bearings may have frozen, in which case your disposal unit has ground its last peel.

The unit suddenly stops

This is usually nothing more problematical than the reset button having been tripped because the motor has overheated. Let the unit rest for a few minutes then press the button back in and switch the unit on again.

If the waste disposal unit keeps tripping its reset switch, there may be something stuck in the unit which is overheating the motor by making work too hard.

If it keeps blowing the fuse/tripping the circuit breaker, you will need a larger fuse, but check first with an electrician - your unit may be too powerful and is trying to draw more current than is safe for house's wiring. If that's the case, a larger fuse could lead to an electrical fire.

The water drains slowly

Try a sink plunger first - that will shift most blockages. If it doesn't do the trick, the trap⁵ may be clogged with solidified fat or an object to large to pass around the bend. Often they have a small inspection panel which can be unscrewed and removed - if not you will have to remove the entire trap from the line. Before doing this it's a very good idea to place a bucket underneath.

Remove the panel and (when the water has stopped coming out) inspect for a blockage. If you can see what's in there, pull it out either with your fingers, or with a pair of pliers if it's being stubborn. Replace the panel and run water through to see if there's a better flow than before.

If there is no inspection panel, take out the entire trap, remove the blockage and clean out the pipe with a bottle brush. Replace the trap and flush water through the unit.

If you found no blockage or if the water is still draining slowly, call in a professional - the blockage is either inside the waste disposal itself, or further down the drain. If you try pushing a pipe snake through the waste disposal you'll most likely do more harm than good.

Slow drainage can sometimes be caused by not enough water being used when grinding. Without sufficient water, the resulting pulp from the ground foodstuffs becomes too thick to flow out through the drain and blocks it up. Simply use more water when grinding.

How did I ever get by without one of these?

A question you may well be asking yourself once you've lived with the convenience of a waste disposal unit. Gardeners may not be too keen on these devices because they wash valuable compost materials down the drain, but if you live in a flat or apartment and have no need of compost⁶, it makes good sense to look after yours.