A kitchen waste disposal unit, often called an InSinkErator after the best-known brand, looks like a simple under-sink appliance. The job is not always simple. It sits between your sink, trap, waste pipe and electrical supply, so a poor installation can leave you with leaks, smells, blocked pipework or an unsafe socket in a damp cupboard.
For a straightforward London installation, most homeowners should expect to pay around £180 to £350 for labour if the plumbing and electrics are already suitable. Supplying a decent domestic unit usually adds roughly £120 to £450, depending on model, size and noise reduction. If new wiring, a spur, pipework changes or cupboard alterations are needed, the total can move into the £450 to £850 range.
The right price depends on what is already under your sink, not just the disposal unit you have bought. We see plenty of Kensington and Chelsea flats where a small-looking job becomes more involved because of old waste runs, tight Victorian or mansion-block cupboards, shared stack pipework or badly placed sockets.
Why Insinkerator Installation Costs Vary Under London Kitchen Sinks
The biggest cost difference is usually access. A modern kitchen base unit with a single bowl sink, a clear cupboard and a nearby safe electrical outlet is far quicker than a cramped cupboard full of old copper pipe, washing machine hoses, a water softener, a shelf and a trap pushed hard against the back panel.
The second issue is the existing waste pipe. Waste disposal units discharge ground food waste into the drainage system, so the fall, trap arrangement and pipe size matter. A badly fitted unit can leave food residue sitting in a flat section of waste pipe, which then smells or blocks, especially in older London properties where the kitchen waste run may already be long and shallow.
The third issue is electricity. A waste disposal unit needs a safe supply, normally controlled by an air switch or suitable wall switch, and protected by RCD. Electrical work in kitchens falls under Part P of the Building Regulations, and any new circuit or significant alteration should be handled by a competent electrician working to BS 7671. If there is any doubt about the electrical side, get it inspected professionally rather than guessing.
Check the Sink, Cupboard and Waste Route First
Start by looking at the sink itself. Most waste disposal units fit a standard 90 mm sink waste opening, but some older sinks, Belfast-style sinks or thin budget stainless sinks need extra checks. If the sink waste hole is too small, damaged or unusually shaped, the job may need a sink alteration or a different fitting kit.
Then check the space below. A typical domestic unit can be around 300 to 400 mm high and quite wide, so it may clash with shelves, drawer backs, stopcocks, boiling water tanks or pull-out bins. In some Kensington flats we have had to trim an internal shelf or alter a cupboard back panel before the unit could sit correctly without pressing on pipework.
Finally, follow the waste pipe from the trap to the wall or floor. If the pipe has a poor fall, too many elbows, old compression joints or a long horizontal run, it is worth allowing for pipework improvement. A small change here can prevent repeat blockages later, which is cheaper than paying for call-outs every few months.
Choose a Unit That Suits the Property, Not Just the Box Price
Entry-level waste disposal units often cost around £120 to £180. They may be fine for light use in a small flat, but they tend to be noisier and less forgiving if tenants or guests put the wrong things down the sink. Mid-range domestic units are often £200 to £350 and usually give a better balance of power, noise control and build quality.
Larger or quieter models can be £350 to £600 or more. These make sense in larger kitchens, family homes or higher-end rental properties where a rattly cheap unit would be noticed quickly. Commercial kitchens are a different matter and need a proper assessment of usage, drainage and hygiene requirements before any recommendation is made.
We would rather fit a sensible unit correctly than put in the most expensive model for the sake of it. A powerful unit on poor pipework still gives trouble. A modest unit on a good waste run, wired safely and used properly, will usually perform better.
Confirm the Electrical Supply Before the Plumbing Is Disturbed
Before removing the old trap or sink waste, check how the unit will be powered and switched. Many installations use an air switch mounted on the worktop or sink, because the electrical switch mechanism stays away from wet hands. Other setups use a suitable wall switch or fused spur, depending on the kitchen layout.
If there is already a socket under the sink, do not assume it is suitable. It should be correctly positioned, protected, in good condition and not exposed to leaks. We often find loose sockets sitting on cupboard floors, overloaded extension leads or old unswitched sockets close to pipe joints, none of which we would leave feeding a new appliance.
If a new fused spur, socket or circuit alteration is needed, allow extra cost. A simple local electrical adjustment might add £120 to £250. More involved work, such as running a new supply, improving RCD protection or dealing with an old consumer unit, can cost more and should be priced after inspection. Our electrical services team can check this properly when the installation needs both trades.
Fit the Mounting Assembly and Seal the Sink Waste Correctly
The old sink waste, trap and pipework need to come out cleanly, not be forced. Once the sink opening is cleaned back, the disposal unit mounting assembly is fitted with the correct seal or plumber’s putty, depending on the manufacturer’s instructions and sink type. This is where rushing the job often causes slow drips into the cupboard.
The mounting ring must sit square and tight. If it is cross-threaded or uneven, the unit can vibrate, leak or loosen over time. On thin stainless sinks, the area around the waste may flex, so the installer needs to check that the sink is rigid enough to take the weight.
Once the unit is hung on the mounting assembly, it should be turned into its locked position without straining the sink or pipework. The body of the unit must not press hard against the cupboard, back panel or neighbouring pipe. A disposal unit vibrates in use, so a few millimetres of clearance matters.
Reconnect the Trap, Dishwasher Hose and Waste Pipe Properly
The waste connection needs a proper trap arrangement, not a collection of mismatched fittings. Most domestic installations use 40 mm waste pipe, with the dishwasher or washing machine connection made through an appropriate spigot if required. Flexible waste hose is best avoided where possible because it sags, holds grease and blocks more easily.
If a dishwasher connects through the unit, the knockout plug inside the disposal inlet must be removed. This is a small detail, but forgetting it means the dishwasher cannot drain. We have attended jobs where the customer thought the dishwasher had failed, when the real fault was a disposal unit inlet still blanked off.
All compression joints should be hand-tightened then nipped carefully, not crushed. The pipe should fall continuously towards the waste outlet. If the trap is too low or the outlet through the wall is too high, the installer may need to rework the pipe route rather than forcing parts to fit.
Test the Unit With Water, Load and Electrical Safety in Mind
Testing is not just flicking the switch once. The unit should be run with cold water flowing, then checked while draining a full sink. Every joint, the sink flange and the dishwasher connection should be inspected with a dry tissue, because a tiny seep is easier to spot before the cupboard is filled again.
The air switch or wall switch should operate cleanly without sticking. The unit should start smoothly, run without excessive vibration and stop without knocking the pipework. If the lights flicker, the breaker trips or the socket feels warm, stop using it and call an electrician.
A professional should also check that the installation has not created a foul smell route from the drainage system. The trap seal must remain intact. In older converted flats with shared stacks, poor trap arrangements can send smells back into the kitchen even when there is no visible leak.
Budget for the Whole Job, Not Just the Appliance
As a practical guide, a like-for-like replacement of an existing waste disposal unit is often around £150 to £280 labour, assuming the old unit comes out cleanly and the electrical supply is sound. A new installation into a suitable sink with minor waste pipe alterations is commonly around £220 to £400 labour. Add the unit itself and typical domestic totals often land between £350 and £750.
If the job needs a new safe electrical point, expect the bill to rise. A combined plumbing and electrical visit in London can easily bring a more involved installation to £550 to £950, especially where parking, access, old fittings or after-hours attendance are involved. Emergency or evening work will usually cost more than a planned daytime appointment.
Landlords should also think about durability and tenant use. A very cheap disposal unit can be a false economy if it jams repeatedly because someone puts onion skins, rice, coffee grounds or bones through it. For rental properties, we usually suggest a robust mid-range unit and clear usage instructions left in the kitchen.
Plan the Timing and Know When DIY Stops Being Sensible
A straightforward installation normally takes two to three hours. A replacement can be quicker if the old unit is not seized in place. A first-time installation with electrical work, cupboard adjustment or waste pipe correction can take half a day or more.
DIY may be reasonable if you are only replacing the rubber splash guard or cleaning a jammed unit with the manufacturer’s supplied tool after isolating the power. It is not sensible to DIY new electrics under a sink, alter fixed wiring, guess at RCD protection or leave a socket where it may get wet. It is also risky to cut into waste pipework if you are not confident about traps, fall and appliance connections.
There are a few warning signs that you should stop and call someone in: repeated tripping, burning smells, water near electrics, a sink flange that will not seal, a unit that vibrates heavily, or a waste pipe that backs up when the dishwasher drains. For those situations, a combined plumbing and electrical visit is usually cheaper than repairing water damage after a failed attempt. Kensington Maintenance Services Ltd can handle this through our plumbing services and electrical team, so the installation is checked as one complete job rather than split between trades who never see each other’s work.
Frequently Asked Questions
Q1: How much should installing an insinkerator cost in London?
For a standard domestic job, expect around £350 to £750 including a reasonable unit and labour. If new electrics, awkward pipework or cupboard alterations are needed, £550 to £950 is more realistic.
Q2: Can an InSinkErator be fitted to any kitchen sink?
No. The sink needs a suitable waste opening, enough strength around the outlet and enough cupboard space below. Some older, ceramic or unusually shaped sinks need extra checks before a unit is bought.
Q3: Does a waste disposal unit need an electrician?
If there is already a safe, suitable supply, the electrical work may be minimal. If a new socket, spur, switch or circuit alteration is needed, use a competent electrician because kitchen electrical work must meet Part P and BS 7671 requirements.
Q4: Will an insinkerator block my drains?
It should not if it is fitted to suitable pipework and used correctly with plenty of cold water. Problems usually come from poor waste fall, too many bends, grease, fibrous food, rice, pasta or tenants treating it like a bin.
Q5: Is it cheaper to repair an old waste disposal unit or replace it?
If it is jammed or needs a small part, repair can be worthwhile. If it is leaking from the body, corroded, noisy or repeatedly tripping, replacement is usually the better spend.
The fair cost of installing an InSinkErator comes down to the unit, the pipework, the electrics and the amount of working space under your sink. If you want it fitted without leaks, nuisance smells or unsafe wiring, ask Kensington Maintenance Services Ltd to inspect the setup and price the job properly, or get a quote from our team before buying a unit that may not suit your kitchen.