Kitchen and lavatory trap sizes

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Moby

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My local plumbing store claims that code says that kitchen traps should now be 2" and bathroom sinks 1 1/2". At the big-box stores, all 1 1/4" trap kits are labelled "Lavatory," and all 1 1/2" kits are labelled "Kitchen." No 2" trap kits seem to be present at all. Regardless of where I ought to buy my plumbing parts, why the discrepancy?

The people at this supply store tend to lie a lot (claiming chrome-plated brass items are stainless steel, insisting various items are not manufactured just because they don't stock them, and pretending that there is no way to identify a stem of known brand from a photo), so are not a good source of information.
 

Terry

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Kitchen sinks and laundry trays use 1-1/2" p-traps
Lavs use 1-1/4" p-traps. At least that is the size of the tailpiece.
On recent installs, (since the 60's) we use a 1.5" trap with a 1.5 x 1.25 reducing slip joint washer.

A kitchen sink and laundry tray will have a 2" waste line, with 1.5" trap arm.
Most lavs are plumbed with 1.5" on the waste now. It's hard to find suitable 1.25" pipe anyway.
 
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