Macerator discharge pipework query (not actually a Saniflo)

[GwyneeJ]

I'm installing a macerator (like a Saniflo but cheaper) for the en-suite. The discharge pipework is 32mm solvent welded waste pipe, with a 3 metre vertical lift into the roof space and then 8 metres falling by gravity at a gradient of 1:30 to the soil stack.

Question is should I fit an air admittance valve at the start of the gravity section? The instructions don't require it but I'm just thinking it might help the 'gunk' to clear better.

Any thoughts?

[Dicky99]

I'm installing a macerator (like a Saniflo but cheaper) for the en-suite. The discharge pipework is 32mm solvent welded waste pipe, with a 3 metre vertical lift into the roof space and then 8 metres falling by gravity at a gradient of 1:30 to the soil stack.

Question is should I fit an air admittance valve at the start of the gravity section? The instructions don't require it but I'm just thinking it might help the 'gunk' to clear better.

Any thoughts?

You need to apply for Building Regs approval and follow the requirements of the relevant approved documents. If in doubt about application ask the BCO because you'll need to have a completion certificate from him/her on completion for your records.

[Mike4]

I'm installing a macerator (like a Saniflo but cheaper) for the en-suite. The discharge pipework is 32mm solvent welded waste pipe, with a 3 metre vertical lift into the roof space and then 8 metres falling by gravity at a gradient of 1:30 to the soil stack.

Question is should I fit an air admittance valve at the start of the gravity section? The instructions don't require it but I'm just thinking it might help the 'gunk' to clear better.

Any thoughts?

A three metre vertical pipe 32mm in diameter permanently full of sh1t?

Rather in your house than mine, when that box eventually fails!!


If ever there was a piece of machinery in a house NOT to cheapskate on, the Saniflo would be IT, (in my personal opinion). If you really must have one at all.

[kempiejon]

I'm installing a macerator (like a Saniflo but cheaper) for the en-suite. The discharge pipework is 32mm solvent welded waste pipe, with a 3 metre vertical lift into the roof space and then 8 metres falling by gravity at a gradient of 1:30 to the soil stack.

Question is should I fit an air admittance valve at the start of the gravity section? The instructions don't require it but I'm just thinking it might help the 'gunk' to clear better.

Any thoughts?

A three metre vertical pipe 32mm in diameter permanently full of sh1t?

Rather in your house than mine, when that box eventually fails!!


If ever there was a piece of machinery in a house NOT to cheapskate on, the Saniflo would be IT, (in my personal opinion). If you really must have one at all.

Argh, repressed memory from 30 years plus. Chum in a dark grotty basement bedsit with [expletive deleted] muncher. Never heard of such a thing before, not only did it go up it also went all along the wall of the flat - at ceiling height. Then it failed and all came out under pressure. I was just visiting and couldn't just leave them could I.

[tacpot12]

I'm not a plumber and have no expertise in this area, but for what it's worth, I wouldn't install a AAV.

I would say that there is too much risk of it failing (leaking) and raw sewage being pushed out under pressure from the pump. I think it would be better to have a wider pipe for the gravity section, e.g. 50mm, to allow air from the sewer to flow up to the highest point. If the gravity section is left as 32mm, it seems more likely that it could clog under pressure from the pump. I agree that finding a way to get air to the top of the gravity section is a good idea.

This video (at around 9:55) deals with the problem of air on the pumped side of the piping, where air in the pumped side needs to be exhausted to atmosphere: https://youtu.be/eHAsuPVBwYM?si=EXGxKbJKjZH8SR4G

The video gives some insights to the problems you are trying to deal with.

You could also ask your question on this forum where you will get more knowlegeable answers: https://www.ukplumbersforums.co.uk/

[Gwynee]

I'm installing a macerator (like a Saniflo but cheaper) for the en-suite. The discharge pipework is 32mm solvent welded waste pipe, with a 3 metre vertical lift into the roof space and then 8 metres falling by gravity at a gradient of 1:30 to the soil stack.

Question is should I fit an air admittance valve at the start of the gravity section? The instructions don't require it but I'm just thinking it might help the 'gunk' to clear better.

Any thoughts?

A three metre vertical pipe 32mm in diameter permanently full of sh1t?

Rather in your house than mine, when that box eventually fails!!


If ever there was a piece of machinery in a house NOT to cheapskate on, the Saniflo would be IT, (in my personal opinion). If you really must have one at all.

Total volume of the pipe contents will be around 2.5 litres, so less than you might think. And I intend to include a drain plug near the bottom so it can be drained safely into a bucket when necessary.

Unfortunately we have no choice about having a macerator, the en-suite was built with a Saniflo years ago and I hate it! I've tried to think of ways to install a proper 110mm waste, to no avail. We seem to be replacing the Saniflo every 5 years or so, at a cost of about £600, and the cheapo version we have now bought does get good reviews. If it only lasts a couple of years it will still be less costly per annum than Saniflo.

[bungeejumper]

Just for old time's sake, here's a thread from 2018 in which several of us outed ourselves (although I'd escaped the monstrous beast) and shared a few fun stories. viewtopic.php?t=11212

I had a more recent encounter with a plumber who was installing an expensive medical gizmo with a very similar (ahem) purpose and function in one of our commercial properties. He was using 40mm pipe throughout, but he'd chosen right angle elbows rather than swept bends. I asked him why? Because it's neater, he replied. I hope our client won't come to regret that?

BJ