Waste pipes again

[GoSeigen]

The waste pipe from an upstairs bath and basin ideally needs to tee into the waste pipe of the downstairs bathroom. What are the usual ways of preventing the waste water from upstairs backing up into the downstairs bath on the way out? I'm guessing that these may involve a combination of the following:

-shape of the connector
-position of the tee relative to downstairs bath i.e. a certain distance below the bath outlet, or allowing a certain minimum drop before the tee
-using different size waste pipes
-I'd guess non-return valves are a no-no.

Am I on the right track?

Are there other obvious problems to avoid?

GS

[Mike4]

The waste pipe from an upstairs bath and basin ideally needs to tee into the waste pipe of the downstairs bathroom. What are the usual ways of preventing the waste water from upstairs backing up into the downstairs bath on the way out?

The usual way (correct way) is not to do it in the first place. Each waste fitting should have its own separate waste pipe connected to the soil stack or a gulley/hopper.

Teeing waste pipes into each other is a recipe for trouble and possibly contravenes the water regs, although I'm not sure about that last bit.

[88V8]

So if the lower pipe blocks up, it could back into the downstairs bath....yes... is this 50mm pipe or smaller that you're using for the whole job.... the modern way is to tee into the soil & vent pipe /stack pipe, which obviates the problem.

A non-return valve would block up with hair n stuff I imagine.

With a long drop of small-bore pipe another problem is a vacuum sucking the water out of the upstairs traps. There needs to be an external vent to air, like on a stack pipe. Or use an anti-syphon trap like this https://www.manomano.co.uk/waste-trap-and-accessories-for-basins-2373?model_id=33870486&referer_id=691675&msclkid=d751d8d7e9491dab48dcb804e57f6541&utm_source=bing&utm_medium=cpc&utm_campaign=GB%20-%20Bing%20Shopping%20-%20test%20tROAS%20-%20pool%20test&utm_term=4576236126910305&utm_content=A%20-%20Desktop

In our old house I ran both upstairs wastes into a hopper like this https://www.ebay.co.uk/itm/133796296720?hash=item1f26e17810:g:sLMAAOSwMSRfV9vp which then discharged into an open gully, so no connection with downstairs.

Basically no fancification with fittings is going to prevent water taking the line of least resistance - if the lower pipe blocks or is too small it will run into the bath as you say, so if there is no stack pipe you can connect to I'd run two separate pipes. If external I'd use copper - I think they're pretty fond of big copper pipes on the Continent - that would look OK. If internal, plastic.

The upstairs pipe needs to be vented to air, as if it were a mini stack pipe, to break the suction. If the pipe run is internal, to avoid smells use a mini Durgo like this https://www.drainagesuperstore.co.uk/product/flexseal-32-40-50mm-universal-air-admittance-valve.html.

V8

[Dod101]

When I read about all this sort of stuff I get very alarmed because if I were to buy a house I would not expect to have to go and inspect the plumbing to ensure that things were properly done. My answer to GS is to engage a plumber to do the work, especially when dealing with bathroom waste.

Dod

[GoSeigen]

So if the lower pipe blocks up, it could back into the downstairs bath....yes... is this 50mm pipe or smaller that you're using for the whole job.... the modern way is to tee into the soil & vent pipe /stack pipe, which obviates the problem.

[...]

The upstairs pipe needs to be vented to air, as if it were a mini stack pipe, to break the suction. If the pipe run is internal, to avoid smells use a mini Durgo like this https://www.drainagesuperstore.co.uk/product/flexseal-32-40-50mm-universal-air-admittance-valve.html.

Thanks 88V8 and Mike4, very helpful. The venting I hadn't thought through fully, makes perfect sense.

When I read about all this sort of stuff I get very alarmed because if I were to buy a house I would not expect to have to go and inspect the plumbing to ensure that things were properly done. My answer to GS is to engage a plumber to do the work, especially when dealing with bathroom waste.

Don't worry, an expert will do the work, but one needs to do a certain amount of thinking and planning in advance and have a basic understanding of what is possible and what not...


GS

[bungeejumper]

The upstairs pipe needs to be vented to air, as if it were a mini stack pipe, to break the suction. If the pipe run is internal, to avoid smells use a mini Durgo like this https://www.drainagesuperstore.co.uk/product/flexseal-32-40-50mm-universal-air-admittance-valve.html.

Indeed. I was advised to do similar when connecting our shower into an existing washbasin waste. It's always worked fine and imperceptibly. Doesn't vent any smells. Excellent.

BJ

[sg31]

If external I'd use copper -

V8

I wouldn't unless it's above ground floor level.. I've had to replace copper pipes numerous times for people who had them stolen. I can't imagine it being worth the effort but it happens regularly in some areas. Very common in Brighton where the population of drug addicts is quite high. It also happened to my parents house in Sheffield.

It costs much more to replace the pipes than they are worth but the aggravation is worse than the cost.

[88V8]

When I read about all this sort of stuff I get very alarmed because if I were to buy a house I would not expect to have to go and inspect the plumbing to ensure that things were properly done. My answer to GS is to engage a plumber to do the work, especially when dealing with bathroom waste.

Hehheh.
Our previous house from the stopcock on was all me... the domestic water, and the CH designed and fitted including the control system and indeed at one time the gas boiler.
And it worked 30 years without fault.

Our current house, the professional plumbing is a PITA. Unsupported pipes, waste pipes with a drop then no fall that constantly block, and the undersink water heater with the wrong type of pressure vessel that eventually would have rusted and exploded.

The building trade is awash with incompetents.
GS is so right to do his own research as to what can be done and how it should be accomplished, and the same applies to all aspects of building work except perhaps the arcana of electrics.

...Very common in Brighton where the population of drug addicts is quite high.

Oh. And there was me thinking the only thing wrong with Brighton was the interminable pedestrian traffic lights

V8

[Dod101]

When I read about all this sort of stuff I get very alarmed because if I were to buy a house I would not expect to have to go and inspect the plumbing to ensure that things were properly done. My answer to GS is to engage a plumber to do the work, especially when dealing with bathroom waste.

Hehheh.
Our previous house from the stopcock on was all me... the domestic water, and the CH designed and fitted including the control system and indeed at one time the gas boiler.
And it worked 30 years without fault.

Our current house, the professional plumbing is a PITA. Unsupported pipes, waste pipes with a drop then no fall that constantly block, and the undersink water heater with the wrong type of pressure vessel that eventually would have rusted and exploded.

The building trade is awash with incompetents.
GS is so right to do his own research as to what can be done and how it should be accomplished, and the same applies to all aspects of building work except perhaps the arcana of electrics.

...Very common in Brighton where the population of drug addicts is quite high.

Oh. And there was me thinking the only thing wrong with Brighton was the interminable pedestrian traffic lights

V8

Great if you are competent and know what you are doing. I am fortunate that I have good tradesmen I can call on except for roofing work where I simply cannot find anyone who will come when they say they will and then do what they say they will.

Dod