combining waste
- Thread starter Fallout
- Start date
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Not best practice but yes you can.
Anti Vac traps may not be needed but no problem fitting them.
If I ever drop a basin waste into the bath waste pipe, I put a none return valve in just before the Tee, that way nothing will come up the bath from draining the basin.
Anti Vac traps may not be needed but no problem fitting them.
If I ever drop a basin waste into the bath waste pipe, I put a none return valve in just before the Tee, that way nothing will come up the bath from draining the basin.
It comes down to distance from outlets and correct fall levels, water will always run to the path of least resistance downhill.
With a shared bath waste run try to make the waste run 50mm, that way the basin waste water at 32mm with a swept Tee, will not overwhelm the 50mm waste pipe downstream and unless it's blocked/restricted will not cause an issue with backing up to the bath as it will always want to drain down, rather than up hill. Nor will it pull on the bath waste for the same reason, but the bath waste water may pull on the basin seal, due to the much greater flow/capacity past the Tee, hence an anti vac trap for the basin
With a shared bath waste run try to make the waste run 50mm, that way the basin waste water at 32mm with a swept Tee, will not overwhelm the 50mm waste pipe downstream and unless it's blocked/restricted will not cause an issue with backing up to the bath as it will always want to drain down, rather than up hill. Nor will it pull on the bath waste for the same reason, but the bath waste water may pull on the basin seal, due to the much greater flow/capacity past the Tee, hence an anti vac trap for the basin
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Best practice and good design on a new build would cater for separate inlet's into the stack 
Next best would be 50mm (2") shared branch. 40mm (1 1/2")is the smallest you would go and a branch with an AAV at the furthest part of the run, then just anti vac traps and finally would be just 40mm pipe without any vents, getting cheaper as you go.
Just remember that the length and fall is just as important as size especially to the self cleaning aspect of a well designed waste run.
Next best would be 50mm (2") shared branch. 40mm (1 1/2")is the smallest you would go and a branch with an AAV at the furthest part of the run, then just anti vac traps and finally would be just 40mm pipe without any vents, getting cheaper as you go.
Just remember that the length and fall is just as important as size especially to the self cleaning aspect of a well designed waste run.
Yup, seen it a lot....it's other way about, antivac goes on the basin. The bath, given the volume of water and being 40mm to start with, will fill the 40mm waste pipe run, as it passes through the basin tee, it can cause a partial vacuum within the 32mm pipe, therefore pulling on the basin seal. The bath can suffer from self syphoning if the run is long but if the fall is correct (with a good vortex) then this should be minimised.
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