Tee basin into shower waste?

[UserError]

Hello, have a 4m run of 50mm pipe for the shower. The layout of joists, closeness of corner walls etc mean that it would be very helpful to be able to add the basin waste to a swept tee in the shower waste and this could be between 300-800mm from the soil stack . I've read elsewhere very mixed responses to teeing in wastes, some saying it's OK and some saying it'll syphon the water out of one or both traps. I'd value the opinions from this forum. Many thanks.

 

[Ben-gee]

I wouldn’t do it unless there is absolutely no other option - there will be but it may be more work. Take my advice and do the extra work now, then trouble free for years.

 

[UserError]

I wouldn’t do it unless there is absolutely no other option - there will be but it may be more work. Take my advice and do the extra work now, then trouble free for years.

Bum. Thanks. Not a massive amount of work, but it means some somewhat intrusive boxing-in downstairs, but fortunately it's the downstairs loo, so not the end of the workd.

 

[Ric2013]

Bah. On 50mm pipe you may well get away with it, especially if the waste from the basin is a bit restrictive and doesn't allow too much flow. I don't like the concept, but it may be worth physically trying it, testing for siphoning out of wastes and backflow into the shower and if it works then okay.

 

[cjg]

fit a anti siphon trap on basin,

 

[Ric2013]

fit a anti siphon trap on basin,

Anti-siphon traps do work (but we don't know which appliance will induce a siphonage on the other so not sure sure which trap might need one) but can be noisy and normally use a mechanical air inlet component that will eventually fail (though a resealing bottle trap does not have this problem). Fitting such traps to make an existing and defective installation work is perfectly acceptable, but here we are discussing a brand new installation. 50mm shared waste is a bit of a grey area and circumstances will dictate how grey the area is. As 4m is already on the edge of acceptability, my inclination would not be to share the waste, but as this is DIY, the time spent faffing is not chargeable, and field testing might well prove a shared waste to be perfectly serviceable.

Once we're into the realms of fitting air inlets/resealing traps, or anti-siphon devices, this feels very much like a bodge if installed from the outset. Obviously it's up to the OP - and as a DIYer he may be fine with it - but I feel I would be doing my own profession a disservice were I not to try to uphold the standard I would apply to my own work. To me, if the rig only works with one of these devices installed, then it's not a good installation.

 

[UserError]

Anti-siphon traps do work (but we don't know which appliance will induce a siphonage on the other so not sure sure which trap might need one) but can be noisy and normally use a mechanical air inlet component that will eventually fail (though a resealing bottle trap does not have this problem). Fitting such traps to make an existing and defective installation work is perfectly acceptable, but here we are discussing a brand new installation. 50mm shared waste is a bit of a grey area and circumstances will dictate how grey the area is. As 4m is already on the edge of acceptability, my inclination would not be to share the waste, but as this is DIY, the time spent faffing is not chargeable, and field testing might well prove a shared waste to be perfectly serviceable.

Once we're into the realms of fitting air inlets/resealing traps, or anti-siphon devices, this feels very much like a bodge if installed from the outset. Obviously it's up to the OP - and as a DIYer he may be fine with it - but I feel I would be doing my own profession a disservice were I not to try to uphold the standard I would apply to my own work. To me, if the rig only works with one of these devices installed, then it's not a good installation.

Thanks Ric2013. This integrity is why I came here. Yes, I have got time to faff, but I want it to be right as well as fit & forget. It was one of those questions you deep down probably know the answer to but hope...

 

[SimonG]

I wouldn't tee in the basin waste. I dont tee any of my wastes. Not worth the hassle.