installing downstairs wc - syphonage on soil stack consideration?

I'm going to fit a wc below the stairs on the ground floor of our semi, and attach to the same soil stack as the existing FF wc. Is there likely to be a problem with syphonage - such that when I flush the upstairs toilet, the ground floor toilet will gurgle? should I consider putting some kind of vent bypass pipe from the lower section of the stack? I vaguely remember learning about this, but have never seen it done. Perhaps it isn't necessary.
1. Or will it be ok re syphonage?
2. Is a Saniflo macerator a good idea, or is a conventional waste outlet better?
thanks Tony
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tonyjeffs wrote:

Provided that your stack pipe is properly installed, I would not expect a problem with syphonage. (Our ground floor WC is not under the stairs but does connect to the stack pipe which services the upstairs WC and bathroom. No problems. Not even a trace of a ripple on the ground floor WC when the upstairs one is flushed.)
I suggest you look at the archive if this group for general opinion of Saniflo. (Summary: It will need unblocking. Unblocking is extremely unpleasant.) I can't imagine a reason for installing one if a conventional waste is possible.
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Rod wrote:

same here downstairs loo is more or less directly below a bath shower and two toilets with no problems what so ever, you can hear the water in the stack pipe as its internal but you don't get any movement of water in the downstairs loo
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Rod wrote:

Read this as Rod suggests http://www.diyfaq.org.uk/humour.html#saniflo
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On Oct 12, 9:40 am, "The Medway Handyman"

I enjoyed reading 'bout saniflo :-) I guess I'll give it a miss!! Cheers
Tony
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tonyjeffs wrote:

Surely Saniflo is a breach of Trades Descriptions: Sani == Sanitary and Flo == Flow, both of which seem questionable.
Seriously though, provided your waste instalation complies with Building Regs in respect to pipe sizes and open vents it will be fine. In essence make sure it uses 110mm plastic pipe or if it's older then the cast iron equivalent and that there is an open vent within (IIRC) 6 instalations away and preferably on the last installation of a run. In any normal setup these requirements are already easily met and you'll probably find that your pipe to upstairs goes on to roof level where it is open vented. In essence this open venting provides an "easy" path for air to get in so that there is never a negative pressure to induce siphonage. Even if you have an automatic valve upstairs instead you'll probably be fine.
The only other thing you might need to look out for is wether other wastes join the downpipe near your intended join. If so you have some other requirements to meet to avoid backflow. Not hard usually but you do need to meet them.
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tonyjeffs wrote:

Provided that a) the distance to the stack from your new toilet doesn't exceed 6m (or less if there are a number of bends), or b) there is a vent on the existing stack (which there should be anyway for a toilet above the ground floor), then you shouldn't have a problem. Even if you do, you could stick a 'Durgo' valve on the new branch.
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Hugo Nebula wrote:

From memory Hugo I think you couldn't fit a Durgo on the new branch as to comply with regs these need to be installed above the flood level of all fittings so it would need to be higher than the upstairs loo. That's from memory though so the OP might like to check the regs before dismissing the idea. Mind you I suspect it wouldn't be neccessary anyway as I, like you, think he's probably compliant anyway.
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Calvin wrote:

No, it's above the flood level of any appliance _on that stack_ (in this case the new ground floor one).
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On Sat, 11 Oct 2008 20:32:16 -0700 (PDT) someone who may be

Not if you follow the regulations with regard to distances, falls and the like. Make sure no other appliances join the pipe close to the new connection.

Necessary in rare cases, which are extremely unlikely to be encountered in a house. Even if it was necessary in a particular installation there is a lot to be said for avoiding it by, for example, adding another stack. It was done in the distant past when they had less experience of the then fancy new concept of having toilets and basins inside buildings. Toilet pans are unlikely to be affected anyway, it is more likely to be basins.

If gravity drainage can be arranged then it is always better. Simpler, uses no electricity and less likely to go wrong. However, that doesn't mean one should pay much attention to the loud voices of the trolls on the subject. Provided they are properly installed and used macerators work fine. If they are abused they don't, but that is true of many things (including gravity drainage).
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The stack is vented so there shouldn't be any siphon.

If you can fit a normal waste it is better. If you can't a Saniflow is better.
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wrote:

Thanks to everyone. I'll do the drainage the conventional way, not worry about syphonage and give Saniflo a miss.
To
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