Which size waste stack pipe is required?

Which size waste stack pipe is required to service both the kitchen sink, dishwasher,laundry sink and washing machine ?

At the moment it has a 50mm galvanized steel pipe which seems to struggle with the load. It is rusting and needs replacing.

Should I naturally replace with a dwv pvc 50mm pipe or upgrade to 65mm to improve water flow ? Naturally will need to use a reducer at the junction (65mm to 50mm ).

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Accepted answers

bill2

Hi Mitchell

Thanks for your feedback.

Appreciate you taking the timeout to reply promptly.

All the very best.

Bill

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MitchellMc

Welcome to the Bunnings Workshop community @bill2. Many thanks for your question, I'd be happy to answer it.

It would be beneficial to have a larger diameter pipe to increase water flow. If the 65mm length will be several meters it might help with the issue, as the increase in internal diameter will accommodate more of the flow at any one time. However, if you are reducing it back down to 50mm at the junction that will now become the bottleneck. The solution to this issue is to run 65mm to the mains, or alternatively ensure two or more items are not draining at the same time.

Please let me know if you need further assistance or had questions.

Mitchell

bill2

Hi Mitchell

Thanks for taking the time out to respond to my question.

Need to clarify that the draining pipes from the appliances and sinks are 50mm diameters and they are all draining to a stack pipe which is 50mm also. It is this pipe which I am seeking to increase to 65mm to accommodate the maximum load when all appliances and units are operating. So essentially I am increasing the pipe in the water flow direction .

50mm > 50mm >100mm = Existing

50mm > 65mm > 100mm = Proposed

Can't see a problem. Interested to hear your opinion.

Thanks

Bill

MitchellMc

Hi @bill2,

Sorry, I misinterpreted your description. That sounds perfect. If the 50mm was only struggling with a couple of items draining at the same time, then switching it to 65mm will make a big difference. You'll most likely find that if the 50mm gal steel pipe was rusting on the outside, the inside is twice as bad. It might be choked down to a 40mm pipe internally from rust and debris, so switching it out to a larger calibre will make a world of difference.

Mitchell

bill2

Hi Mitchell

Thanks for your feedback.

Appreciate you taking the timeout to reply promptly.

All the very best.

Bill

MitchellMc

It's my pleasure Bill (@bill2).

Please let me know if you need further assistance during the installation.

Mitchell

bill2

Will do.

Thanks Bill

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