Macerator (Saniflo) Installation Guide
A macerator lets you put a WC or bathroom where gravity drainage can't reach — but only where the rules allow, and only if the discharge pipework is run to the manufacturer's limits. Get either wrong and it blocks or backs up.
A macerator — often called by the Saniflo brand name — pumps and macerates waste from a WC, basin or bathroom into a small-bore pipe, allowing sanitary fittings to be installed where a conventional gravity connection to the soil stack is impractical, such as a basement or an en-suite far from a stack.
This guide covers installing one correctly: where macerators are permitted under the Building Regulations, how to run and fall the small-bore discharge to the manufacturer's limits, connecting the WC and any other appliances, ventilation and access, and the compliance and commissioning steps that leave the installation working and recorded rather than blocking on day one.
Key takeaways
- A macerator is for use where gravity drainage isn't practical — Building Regs (Part H) allow it, but there must be access to a gravity WC in the building too, not solely a macerated one where required.
- Follow the manufacturer's maximum pumped distance and lift exactly; small-bore discharge is unforgiving of over-long or badly fallen runs.
- The horizontal discharge run should fall consistently back to the stack, and vertical lift must come before the horizontal run, per the maker's detail.
- Provide isolation, servicing access and the correct electrical supply (fused, RCD-protected) — the unit needs power and will need maintenance.
- Only put down the pan what the unit is rated for; macerators block on wipes, sanitary items and excess paper.
Where a macerator is allowed
Macerators are a legitimate solution under the Building Regulations for situations where connecting to a gravity drain is not reasonably practical — a basement below the sewer, a loft conversion, or an en-suite a long way from the soil stack. Approved Document H recognises pumped and small-bore systems, but the general principle is that a building should not rely solely on a macerated WC where a gravity WC could reasonably be provided; there should normally be access to conventional gravity drainage as well.
Confirm the specific installation is one the regulations and the manufacturer support before committing. Siting a macerated WC as the only WC in a dwelling, where a gravity connection was achievable, is the kind of decision that gets questioned — check the intended use and the drainage options first.
Don't make it the only WC
As a rule, a macerated WC shouldn't be the sole means of foul drainage where a gravity WC could reasonably be installed. Confirm the building has proper gravity drainage available.
Discharge pipe: runs, falls and lift
The small-bore discharge is where most macerator installs go wrong. Every unit has a stated maximum pumped distance and maximum vertical lift, and the two trade off against each other — more lift means less horizontal run allowed. Read the curve for the specific model and stay well inside it rather than at the limit.
As a rule, take the vertical lift first, close to the unit, then run the horizontal section with a slight, consistent fall back down to the point where it joins the existing soil stack or drain. Avoid long flat runs, back-falls and unnecessary bends, each of which slows the flow and invites a blockage. Use the pipe size and fittings the manufacturer specifies.
Doing this on a job? Job diary & scheduling — part of TradePlanr. Free to start, no card needed.
Connections, power and access
Connect the WC pan to the unit with the supplied coupling and connect any additional appliances — basin, shower, bidet — only if the model is rated to accept them and via the correct inlets. Fit isolation on the water supplies and arrange the pipework so the unit can be removed for servicing without dismantling half the room.
Macerators are electrically powered and need a suitable fused, RCD-protected supply installed to BS 7671 — in a bathroom that means correct zoning and protection. Leave proper access to the unit; it is a pump with moving parts and will eventually need cleaning or repair, so building it into an unopenable boxing stores up trouble.
Ventilation, commissioning and use
Follow the manufacturer's requirements for venting the discharge system so the pump isn't fighting air-lock or siphonage, and make sure the connection into the existing drainage is properly trapped and sealed. Once installed, commission it: run water through, operate the WC, and confirm it macerates, pumps and clears without backing up or over-running.
Finally, brief the customer on what can and can't go down it — a macerator handles waste and toilet paper, but wipes, sanitary products and excessive paper are the classic causes of a blocked, stalled unit. Setting that expectation prevents the majority of early call-backs.
Quote and record it properly
Build the macerator quote in TradePlanr with the discharge run, electrics and making-good as separate lines, and store the commissioning notes on the job so the install is evidenced.
From guidance to action
Frequently asked questions
Can a macerator be the only toilet in a house?
Generally no. The Building Regulations expect a building not to rely solely on a macerated WC where a gravity WC could reasonably be provided — there should normally be access to conventional gravity drainage as well. Macerators are intended for situations where gravity drainage isn't practical, not as a default replacement for it.
How far can a macerator pump waste?
It depends on the model, and horizontal distance trades off against vertical lift — more lift means less horizontal run. Every unit has a stated maximum pumped distance and lift; take the lift first, then fall the horizontal run gently back to the drain, and stay well inside the manufacturer's limits.
Why do macerators block?
Almost always because the wrong things are flushed. A macerator handles waste and toilet paper, but wipes, sanitary products and excessive paper jam the cutter and stall the pump. Long, flat or over-long discharge runs also encourage blockages, which is why the pipework must follow the maker's limits.
Related guides
Bathroom Installation Guide
Install a bathroom start to finish — planning, first-fix, water-regulations compliance, second-fix, testing and pricing the job in stages.
The Water Regulations 1999 Explained
Fluid categories, backflow prevention and notification — the Water Fittings Regs in plain terms.
Wet Room Installation Guide
Tanking, floor falls, drainage and waterproofing — how to build a wet room that never leaks.
