New toilet 82mm soil vs 110mm

Discussion in 'Plumbers' Talk' started by Fisnik, May 19, 2019.

  1. Fisnik New Member


    We've got an old larder space that we're thinking of converting to a downstairs toilet and sink. Trouble is it's in the middle of the house with no soil pipe nearby. We were initially thinking of putting in a Saniflo (or a Wasterflo WC2 rather). But anyone you talk to seems to say to avoid macerators. I'd much rather have a normal toilet if possible.

    There's a possible route through under the kitchen units as there's a 140mm high gap underneath them.

    Initially it'd be a 1.5 meter unrestricted run from the toilet into a 90 bend then the only way is through under the kitchen units for another horizontal run of 4.5 meters all the way out of the house. After that another 3 meter run to a sewer drain cover in the back garden.

    The main problem is the run under the kitchen units as in theory with 110mm pipe I'd only have 30mm height difference under the kitchen units. It would mean a drop of 30mm in 4.5 meters which is less than 1 in 100. I would need a minimum of 45mm to achieve 1 in 100.

    If I were to use 82mm pipe it would give me 58mm to play with and I'd be able to get a much better drop. Perhaps 1 in 75 which would be ideal.

    What would be better 110mm pipe with less drop or 82mm pipe with a better drop? According to the regs 82mm is ok to use as long as it has a single toilet on it and the toilet outlet is less than 80mm? I've looked at toilets online and there's no mention of the outlet size in the specs. Are these toilets common? Any suggestions?

    Also the other things is 82mm pipe seems to be rare and expensive... also the fittings seems hard to get hold of. Maybe I'm looking in the wrong place but £30 for 3 meters of straight pipe and over £15 per fitting seems expensive.

    What do you guys think? Any suggestions are much appreciated.
  2. KIAB Super Member

    Larder does it have outside wall,if so any manhole close by.
  3. Fisnik New Member

    No it doesn't. The old larder is in the middle of the house, none of the walls is an outside wall due to an extension built on the side in order to extend the kitchen. You'd have thought the previous owners would have put in a toilet back then but it was a long time ago.
    Last edited: May 19, 2019
  4. ecoplumbing Active Member

    You're correct with 82mm pipe, yes you're ok to use it and yes it's a lot more expensive! Problem is if I've worked it out correctly, you still wouldn't have enough fall to comply with regs. 18mm per metre is minimum fall so you'd need 81mm over 4.5m.
    If it's a diy job with no building inspector then it's you're choice if you want to risk it, I'd make sure there's an access point where it joins into the main soil stack. Macerators are fine if they're installed properly and not misused, just depends if you can cope with the noise!
    KIAB likes this.
  5. Fisnik New Member

    Many thanks. That's good to know about the macerators as it may come to that.

    I'll do the majority of it myself with some help from mates. Is 18mm per metre the minimum or is it the ideal drop? From what I've read they say a drop of no less than 9mm per metre or 1 in 110 and no steeper than 25mm per metre or 1 in 40 as if it's any steeper the water would get away too quick and the solids would get stuck.

    Definitely putting an access point as soon as it comes out under the kitchen units although again finding the usual fittings in 82mm seems a chore in itself. If anyone knows a good store please provide a link.

    Is it worth laying everything else in 110mm and reducing to 82mm the part under the kitchen units and then increasing it again or is that pointless. How about the toilet pan or just put any normal toilet and reduce it down if I have to?
  6. jimoz Screwfix Select

    I've gone 12.5mm per metre i.e. 1:80 underground. Not sure if this gradient is acceptable for 82mm pipe but is for 110mm
  7. Fisnik New Member

    Was wondering about that too. Whether 82mm pipe has different minimum gradient but can't find any material that states so.
  8. ecoplumbing Active Member

    If you're going to use 82mm then it needs to be reduced on the pan connector. All toilets will be 4inch so get a reducing pan connector then pipe the rest in 82 until it joins the main stack. James Hargreaves will sell 82mm pipe or you can shop online and find it cheaper.
    1 in 40 gradient is advised for underground drainage ( 4, inch,) above ground has different regs for some reason. It states between 18mm and 90mm per metre so 18mm is the minimum. There are things you can do to help, increase the water level in the toilet cistern to create a better flush. Try and keep change of direction on the soil pipe to a minimum.
    Fisnik likes this.
  9. ecoplumbing Active Member

    82 and 110 has the same rules regarding gradient . There are some exceptions but generally it's the same. 110mm underground drainage has different rules than above ground
  10. ecoplumbing Active Member

    Just to clarify, are you thinking of running a pipe straight into a manhole or will it connect to a soil vent pipe 1st?
  11. Fisnik New Member

    Still need to lift the manhole to check it but the 110mm would run straight into the sewer manhole in the back garden. Is it ok to fit a Durgo outside just before it goes in the ground by the back wall? Or may have to find a way to put it inside somewhere.

    If I go with the macerator I was thinking of just drilling into the downpipe in order to connect it in.
  12. ecoplumbing Active Member

    If there's no vent pipe already then you'll need to install one on the outside wall, then obviously connect that into the manhole. Can fit a durgo valve on top of the new pipe , just make sure it's higher than the toilet or basin if you're fitting one.
    Fisnik likes this.
  13. Fisnik New Member

    Ok that’s clear. Many thanks.
    ecoplumbing likes this.

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