Trap design

[DanGB]

Hello.
Im re-doing the kitchen and the 40mm waste pipes.

I am confirming here the best way to add a trap into the waste system here for the dishwaher.

Is the picture below the bwest way to do this? The green line is a S-trap. Ive read some bad things about S-traps but this seems to fit?
The pipe going to the outside drain doesnt go into the drain itself but just hags outside above the drain grill.

Thanks.

 

[Hugh Jaleak]

Standpipe and connect to waste pipe, although I'd be concerned about 3 appliances into one pipe. Personally I'd either put in a new waste pipe just for the dishwasher, or upgrade the T and pipework through the wall to the drain to 50mm.

Also extend the pipe outside to discharge under the grip. (Cut a hole appropriate size in the grid to allow the pipe to pass through.)

 

[DanGB]

Thanks for your replies.

So the S trap + standpipe as per the diagram is good to use?

But why would you be concerned about running three appliances through the one pipe?

What would the benefit be of extending the waste pipe through the drain grill? Weve just moved into this house and i think its been like that for years.

 

[Hugh Jaleak]

Sink/washing machine/dishwasher waste's gunge up over time, reducing the available internal bore of the pipe, thus its carrying capacity. In the rare event of 2 or even 3 discharging at once, there is a question over the ability of the pipe to carry the flow, and it soon overtops the standpipe.

Use a standpipe, such as http://www.screwfix.com/p/floplast-washing-machine-trap-white-40mm/18640 and then a 90° bend to get into the tee.

Its advised to extend the waste below the grid as it stops crud, soap, food scraps etc, building up on the grid, eventually blocking it, and the full force of the flow is then available to wash the gulley when an appliance discharges.

 

[Aquaheat]

Standpipe and connect to waste pipe, although I'd be concerned about 3 appliances into one pipe. Personally I'd either put in a new waste pipe just for the dishwasher, or upgrade the T and pipework through the wall to the drain to 50mm.

Also extend the pipe outside to discharge under the grip. (Cut a hole appropriate size in the grid to allow the pipe to pass through.)

If there one thing I've learnt from here it's that you get no thanks from giving good advice. If it's not what they want to hear then they will go elsewhere.

OP, run 3 appliances on a 40mm waste, the S trap will be sound and we will help you when you have damp walls and water from under the units. I hope you are planning to use compression waste too as the solvent weld stuff is so over rated as are brackets, the correct fall, correctly sized pipework, correct water seals, preventing siphoning and doing a job properly.

See that's how you do it @Hugh Jaleak why waste your time for free when you get asked for advice it's then questioned and you get no thanks for it.

Jon

 

[DanGB]

@Aquaheat not sure what that's all about.

I come on the forums for good advice but also to learn.
I was questioning the replies because I wanted to learn the reasoning behind the answers. If I know all this then in the future I can return the favour and help others out.
I normally thank people for the replies too, but obviously not yours because it did not add anything constructive.

Dan

 

[Hugh Jaleak]

Aquaheat, we can but try. If the advice falls on deaf ears then all we can say is we did try and tell you!

Dan, you really need to get rid of that compression tee, and do the job in solvent weld pipework, it is far superior. My other points also stand, but at the very least now if you don't upsize the pipework, change the elbow where the pipe goes through the wall, (and any elbows externally), for a swept bend(s), to assist the flow of water.

Washing machines and dishwaters pump the water out at a fair old rate, the reasoning for using a 40mm waste at a minimum is to be able to cope with the flow from one appliance, and you have 2, plus a sink on the one pipe. Chances of all 3 discharging at once are probably slim, but there is a possibility.

 

[DanGB]

Thanks @Hugh Jaleak
Im rethinking the whole thing now thanks your advice.

I do like solvent weld stuff, the only reason I used the compressed Tee was for easy access to take apart etc, but I see its not really necessary.

Im thinking now to use a reducer [to expand] the pipes coming from the WM/Sink to 50m and add a 50mm Tee where the DW joins the piping, like you said, and the rest of the pipework will be 50mm solvent weld.

 

[Hugh Jaleak]

I know its a bit of extra work, but if it avoids a flood in future then worth the effort now. If there is a fair run of pipe maybe think about installing a cleaning eye where necessary too. Solvent weld doesn't lend itself to being taken apart in the event of a problem.

 

[DanGB]

Well im doing everything from new so might as well do it properly. In my photo above nothing is actually working or stuck together, it was just a mockup of a potential design.

 

[Hugh Jaleak]

We know how we'd do it, so try and advise you the same way, understandably, not everyone is confident in some of the processes involved, but we can all learn. Hopefully you will then have the satisfaction of a job well done too.

 

[DanGB]

@Hugh Jaleak Ive taken your advice and knocked something up. Would value your opinion.

Washing machine and then sink. Total length of 40mm section about 3.5metres.
Where dishwasher meets waste it turns into 50mm and then goes outside to the drain as 50mm approx 2metres.

Its actually a similar layout to how it was before I ripped it out, but it was all 40mm and after the sink it took and outside route to the drain (unsightly)

Thanks.

 

[Hugh Jaleak]

That's your planned final setup? Looks a good job, just ensure there's sufficient fall on the run, plenty of clips to support it and get rid of that poxy compression tee! You seem to be able to work with solvent weld, no need for it! Advise an anti vac trap on sink, just to make sure it doesn't get pulled when washing machine discharges.

 

[DanGB]

Yep that's the plan. Probably going to be 40mm fall per metre.

you really hate those compression fittings don't you

Good idea about the anti vac trap. The sink is a 1 and a 1/2 bowl Ikea jobbie that comes with its own drainage kit, but im thinking of ditching it and making my own as it fits a bit awkwardly. I can then fit a anti syphon trap of some sort.