Am I correct saying, all drain pipes used by wash machine should be 2" pipes.

I need to do the drain pipes for the wash machine in coming weekend, here is the layout:

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Please advice

from what I have gathered from the expert advice on this site, the drain line, p trap and stand pipe all need to be 2 inch pipe and the vent line can be 1.5 inch. Hope this helps. I am sure others will respond to confirm this advice.

make sure that what you do is in accordance with your local code.

in massachusetts, we are allowed to use 1 1/2" pipe for a washing machine drain. we can not, however, drain another fixture into the vent for the washing machine.

ok code says you can use 1 1/2" for it but with the high out put of todays washers most will install 2".

and with the high output i dont think i would wet vent a sink over it. i would tie that into the toilet vent personally. also i hope you are not wet venting the washer on the toilet as this is against code (here)

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Yes, and even if you did not NEED to install 2" it would still be wise to do so. You also have to be aware that the washer's standpipe length is limited and yours may be too long.

Wet venting a sink over it is fine, you just don't want to wet vent the sink below the washer connection.

not in massachusetts. you can not wet vent nor wet vent with a washing machine.

As I have said before, "There are a lot of things you cannot do in MA. About the only thing that is legal is to drive your car off a bridge and let your passenger drown."

only legal if you are a US senator. or, in a more recent incident, if you are $10,000 contributor to the state attorney general who is running for governor of massachusetts.

As Yakov Smirnoff would say, "What a state!"