Macerator toilets and pumped waste units: how they work and how to look after one

A macerator is a small pump unit that sits behind or next to a toilet. It chops up waste and pumps it through a small-bore pipe to the main soil stack or drain. That means a toilet, basin or shower can go in places where an ordinary gravity drain cannot reach, such as a basement, a loft conversion or a room far from the soil pipe.

Many people call any macerator a "Saniflo", after the best-known brand. Other makers sell similar pumped waste units. This guide covers the type, whoever made it. For your own unit, the maker's manual is what counts.

How a macerator works

An ordinary toilet relies on gravity. Waste falls through a large pipe, usually 100mm or 110mm, to the soil stack. A macerator works differently:

1. The toilet flushes into the macerator box instead of straight into a soil pipe.
2. A float or pressure switch senses the water level and starts the motor.
3. Spinning blades break up the waste and toilet paper.
4. A pump pushes the mixture through a small-bore discharge pipe, often up and then along to a soil stack or drain.
5. A non-return valve stops the waste flowing back into the box.

Some units only take a WC. Others have extra inlets for a basin, shower or bath. Some shower and basin units have no macerating blades at all and only pump grey water.

Where they are used

• Basements and cellars, where the room is below the level of the drain.
• Loft conversions and extensions that are far from the soil stack.
• A cloakroom under the stairs where there is no room for a large pipe run.
• Utility rooms and annexes.

They are usually the second choice. Plumbers and building control generally prefer a gravity connection where one is practical. Drainage work falls under Part H of the Building Regulations in England, and Wales has its own version. Read the Approved Document H page on GOV.UK and ask your building control body or installer what applies to a new installation. Many installations also need an electrical supply to suit the location. That connection is for a qualified electrician, and Part P applies in England.

What can go into one

Macerators are much less forgiving than an ordinary toilet. In general, only toilet paper and human waste should go into a WC macerator. Keep these out:

• wet wipes, including "flushable" ones;
• sanitary products and nappies;
• cotton buds, dental floss, cotton wool and kitchen roll;
• hair, fats, oil and food;
• strong chemicals or solvents not approved by the maker.

Put a small bin and a clear notice in the room, especially if guests use it.

Looking after it

Exact steps vary by model, so follow the maker's manual. In general terms:

• Descale regularly in hard water areas. Limescale builds up on the blades, switch and non-return valve. Most makers sell or recommend a descaler made for their units. Use only that, as the manual says. See limescale for hard water background.
• Do not pour in ordinary drain cleaners or bleach unless the maker says they are safe. Some damage the seals and membranes inside.
• Listen to it. A unit that runs for longer than normal, cycles on and off by itself, or makes a new grinding noise is telling you something.
• Flush it now and then if it is rarely used. Waste water left standing smells and lets scale form.

Before anyone works on the unit, it must be switched off and isolated at its electrical supply. Opening the box is a dirty job and not one to start without the maker's service instructions.

Common symptoms and what they usually mean

It runs on, or starts by itself every so often. A worn non-return valve can let water run back into the box. A sticking switch or a dripping cistern can also do it. Check the toilet cistern first. See a running toilet.

It hums but does not pump. The blades may be jammed by something that should not be there, or scale has seized them. Switch it off at the supply. Do not keep pressing the flush.

It smells. A leak at a joint, a poor seal at the pan connector, or waste left standing are common causes. A smell near the toilet base can also be the pan connector. See WC pan connectors.

Water comes back into the shower tray or the pan. The unit may be blocked, the discharge pipe partly blocked, or the non-return valve failing.

It trips the electrics. Leave it switched off and call a qualified electrician or the maker's service agent.

When to stop and call a plumber

Stop and call a plumber or the maker's service team if:

• the unit is blocked and the toilet will not clear after one careful attempt;
• you would have to take the cover off or disconnect the unit to clear it;
• the smell comes from inside the wall, the boxing-in or the floor;
• water is leaking from the unit or the discharge pipe;
• the unit trips the electrics or has stopped completely.

Pouring in more chemicals, or plunging hard, can push a blockage further into the small-bore pipe. That makes the job bigger. Our guide to a blocked toilet covers ordinary WCs, but much of its plunging advice does not suit a macerator. Check the maker's manual first. Hiring a plumber explains how to find someone. Some plumbers specialise in macerators, and makers often list approved service engineers.

Products at Wickes

We haven't tested these. They are examples, with what the retailer's page says.

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

Can I use bleach in a macerator toilet?

Only if the maker's manual says so. Some cleaners and drain chemicals damage the seals inside. Most makers sell a descaler for routine care.

Why does my macerator keep turning on by itself?

Often the toilet cistern is letting a trickle of water into the pan, or the non-return valve is letting water drain back. Check the cistern first. If it continues, ask a plumber or the maker's service agent.

Can a macerator take a shower and basin as well?

Some models have extra inlets for a basin, shower or bath, and some are made only for grey water. Check the model's specification and ask an installer before buying.