Help with fixing Plumbing Macerator waste from Garden office

8 Jan 2008
Reaction score
United Kingdom

Can someone advise me on how I should proceed with this. I had a builder do a garden office for me and toilet for me. He put in a macerator for the toilet (insisted we need one). But he has left it unfinished and I don't think he is coming back and I will have to fix it or get someone else in. I think he made some mistakes and complained, but he wast having it. Please have a look at the photos.

So the 32mm waste pipe exits the macerator horizontally and then exists the building with a 90 bend. It flows along a 15meter trench to the decking where there is two 45 degree bends that rise the waste up above ground level where it goes under the decking before two more 45 degree bends cause it to drop again to connect with the main 110mm drainage pipe that leads to the manhole.

Exit From Office.jpg Run up Garden.jpg Rise up to decking.jpg

I told him a 90 degree bends will cause trouble with macerators (according to installation instructions)
Secondly you cant have a second rise so far a way. Water doesn't flow up hill. He said it will be pumped.
Finally I have concerns about burying the 32mm under ground.

Hopefully someone can advise. As I need this connected and filled in next week before a family event.
Sponsored Links
The 15m length needs the required fall on it and even if the pump could deal with rise at the end of the run it won`t last for any length of time.
Wouldn`t worry about the sharp 90 elbow because A) It is close to the pump and B) It`s really when 22mm pipe is used and they tend to block.
ok so I can leave the 90 bend in place, but I need to remove the rise at the end and just have the required fall from accros the 15m.

What about burying this type of pipe. There are no issues there?
ok so I can leave the 90 bend in place, but I need to remove the rise at the end and just have the required fall from accros the 15m.

What about burying this type of pipe. There are no issues there?
TBH I would probably use 40mm pipe and a drop of around 15mm per m, as for the pipe I can`t advise as I`ve never buried pipe underground.
Sponsored Links
Surely those fence posts have been undermined?
I'm sure this work falls under building regs? What are the requirements...
At the moment I'd imagine it will all be prone to freezing.
How deep is the water service pipe?
Pipe will be ok being buried, as long as nothing damages it. If you can get a fall on it across the garden, does beg the question why it wasn't laid in 4" in the first place. Where does it discharge?
The water pipe is already burred 4ft below the garden, its a blue MPDE. The pipe in picture is for waste water from macerator. Its connecting into a brown 110 underground drain pipe that discharges into the house main manhole. Im told this doesnt fall under regs but i no longer trust this builder.

Its primary function is an office/kids play room but Mrs wanted the option of using it if we ever needed to put the occasional visitors up. Hence the toilet. I dont think it will be used much but still I think we will have issues.

I looked last night and the fall isn't there. From the pipe exiting the office to the junction with the brown pipe is almost level. So underground isnt an option unless I leave the vertical rise in the pipe as they have done it. But to me that seems bad, as not all the waste water will be pushed up especially after travelling 14mtrs. I am sure some will fall back and settle at the bend. Is this correct?

If I lay the pipe overground should I change it to a grey pipe?
Will the macerator push the water 15m to the brown pipe with no fall or should I put in a 45 degree bend up and rise it up to achieve the fall at the exit of pipe from office?
Finally anything I can do to prevent it freezing. i was thinking of boxing it in and covering with insulation.

Thanks again for any help.
Last edited:
What type is the macerator ? Do you have a data sheet for it that provides information about lift ( the hieght it can pump to ) ? Os it a postive displacement pimp or a centrifugal type.

The pipe work you seem to have would not be a problem for a positive displacement pump (*) but may be too long for a centrifugal type with only interrnittant use.

(*) Positive displacement pumps..... our whole house macerating pump worked into 35 metres of 1.25 inch ID pipe with a circa 1 meter lift without any problems. With a positive diplacement pump the pressure created can be high ( 3 bar) and any joints in the pipe need to be able to withstand that pressure. A continuous unjointed pipe should be used.
Last edited:
I would say that unit has a centrifugal pump and the height and distance figures given need to be obeyed. A steep rise 14 metres from the pump would not comply with the data provided.

I very much doubt a centrifugal pump would cope with that rise.
thats what I figured. So rise would need to be at start which means pipe needs to be layed over ground.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links