4" Soil Pipe for Sink in Island?

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apple1

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Hi,
I'm just about to fill rmy ising walls with hardcore & pour subfloor. Ahead of this I obviously had my plumber (apprentice) run out some pipes through the walls for waste water etc. I plan on having a sink & dishwasher in our island and noticed last night that he has ran a 4" waste pipe for this from the approx. island location to the external wall. Is a 4" pipe necessary to take away water from a sink? Thanks in advance, apple1
 
perhaps he has left the 4" to take both the sink and dishwasher....

usually they both would be 2" anyway...

im not a plumber so i may be way out....
 
Hi There. I have the same setup in my place and have a 4" pipe laid to take away the waste water. Makes it easier to rod if it gets blocked. Also don't forget you might need to run some hydra under the floor for hot/cold supply to your sink and dishwasher. In my case I also had to put in some ducting to run a gas pipe to my cooker.
 
The waste for either a sink or dishwasher will be 40mm (and not 2"), it would be good practice to have this discharge to a 4" drain where this drain will be underground. As already indicated it makes life a lot easier if there is ever a blockage and there will be- grease will build up over time. Your plumber can fit the 4" waste with a rubber grommet to accept a 40mm waste upstand and this can cater for both sink and dishwasher wastes. The waste upstand (with sink trap with spigot for dishwasher waste connection) will be trapped to prevent sewer gases from entering the kitchen. I'm only a "hobby plumber" but I have a similiar set up in my own kitchen and it works very well. It's generally frowned upon to bury 40 or 50mm wastes underground or in concrete, except when space restriction make it inevitable.
 
Thanks Carpenter. I read your posts with interest and find it reassuring that the fitting the 4" pipe is indeed the correct method.
 
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