Macerators and pumped WCs

What they solve

A WC needs a large-bore soil connection with a consistent fall to the stack. That is what makes moving a WC expensive and what makes some positions impossible – a cloakroom under the stairs, an en-suite in a loft conversion, a basement, an outbuilding, anywhere below the drain invert level.

A macerator removes the constraint. It grinds the waste and pumps it through small-bore pipe, which can run at a shallow fall, uphill, and around corners that a soil pipe could not manage. That opens up positions gravity simply cannot serve – see bathroom layouts and soil pipes.

The honest limitations

• They need power, and if the power fails the WC is unusable.
• They are audible. A macerator running is a distinctive noise and it carries. Not a problem in a downstairs cloakroom; more of one in an en-suite next to a bedroom.
• They are sensitive to what goes down them. Waste and paper only. Wipes, sanitary products, cotton buds, dental floss and kitchen roll all block them, and wipes are the single biggest cause of failures.
• They are a mechanical item that will fail. Not if, when. A blade, an impeller, a pressure switch or a motor, eventually.
• When it fails, the WC is out of use until it is repaired – unlike a gravity WC, which will keep working through almost anything.
• Building Regulations generally expect at least one WC in a dwelling on gravity drainage, so a macerator is normally an addition rather than a replacement for the main WC.
• Some buyers and surveyors view them unfavourably, which is worth knowing if you may sell.

Types

Where no WC is involved, a simple greywater pump is considerably more reliable than a macerator, because there is nothing to grind and nothing to jam. If your problem is a basin and a shower rather than a WC, ask about that instead.

Installing one so it can be serviced

This is where most macerator installations fail, and the failure is entirely predictable: the unit is boxed in behind tiling with no access, and then it needs servicing.

1. Design the access firstA removable panel large enough to withdraw the unit, not a hand-sized hatch. This is the single most important decision and it is the one most often skipped.
2. Isolation on every inletSo the unit can be worked on without draining anything.
3. A non-return valve on the dischargeTo stop backflow into the unit.
4. Correct discharge pipe size and routeFollowing the manufacturer’s maximum vertical lift and horizontal run, which reduce each other. Exceeding them means a unit that struggles and eventually fails.
5. A vertical rise first, then horizontalWhere the manufacturer specifies it. Getting the order wrong causes the pipe to hold waste.
6. Connection to the soil stack at the right pointWith adequate separation from other connections.
7. A dedicated electrical supplyWith an accessible isolator – because the first thing anybody needs to do when it misbehaves is turn it off.
8. Ventilation of the unitPer the manufacturer, and a proper WC connection so the pan seals correctly.

Living with one

• Waste and paper only. Put a note somewhere if guests use it – wipes are the single biggest cause of failures and ‘flushable’ wipes are not.
• Descale periodically in a hard water area, with a product the manufacturer approves. Scale on the blades and the impeller is a real factor here.
• Do not put bleach or strong chemicals down it unless the manufacturer says so – some attack the seals.
• Listen to it. A change in the noise, a longer run time, or a unit that cycles on its own all mean something.
• Do not ignore a slow flush. It is the early sign of a partial blockage, and dealing with it early is far easier.
• Keep the isolator accessible and know where it is.

Treated sensibly they last well. Treated as an ordinary WC that will swallow anything, they do not.