We are installing a new master bath in our home. We are planning to install a vanity with double undermount sinks with granit counter tops. The room is 68" wide where the vanity is planned. Is it standard practice to have one drain coming out og the wall and then branch off (y) to each sink trap or have two separate drains coming from the wall, each going to its separate sink. Our decision may have a bearing on the configuration of the vanity drawer placement.

It is standard practice to rough in a separate drain and water lines for each sink. Both sinks can vented with one vent from the top of a cross with a branch to each sink from the cross. You can also use a double y instead of a cross, but in my code area this is not a legal vent, in some places it is.

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It is standard practice to rough in a separate drain and water lines for each sink.

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Puff, you have two stubouts coming out of the wall for one vanity with two tubs? WHY?
In my area (Tampa Bay) we only run one stubout out of the wall. If it'
S in the contract we wye off to two traps but as a rule we user one trap and connect both tubs with a contentious wastr,(see image). I can see no advantage to having two stubouts for one vanity. Regards, Tom

Tom:
The images that you show are only used for double bowl kitchen sinks in this area, and how would you use it if there are drawers between the vanity sinks? Here we rough out twice or as poster asked, rough out once and pipe in the cabinet to second sink.

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rough out once

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Gee Puff, Did I
Misunderstand when you posted,

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It is standard practice to rough in a separate drain and water lines for each sink.

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I'm sorry! I took the to mean two stubouts coming out of the wall.

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how would you use it if there are drawers between the vanity sinks?

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In that case ,(as I've already posted) we would wye off with two traps. But most of the vanities we have plumbed only have a ledge so a contentious waste will work just fine. Sorry about the confusion I just didn't understand When you said,

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rough in a separate drain

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My bad! Cheers, Tom

Tom:
You didn't misunderstand. We rough out twice for double vanities, approximately 2"-3" off center or on center of each sink. If the vanity is a 5' vanity the sinks would be 30" apart center to center if they are centered on vanity. It sounds like this vanity might be 68" which would place the sinks even farther apart, that would mean using extension pieces with a continuous waste. Sorry if you misunderstood me or if I am misunderstanding you. Piping in vanity is not a standard practice here, but can be done that way if necessary. To me it is easier to rough out twice with a cross if wall is open and not drywalled, it it is drywalled and already has a waste roughed out then it would be piped in vanity.

In my area, if the sinks are within 30" center to center of drains I can use a continuous waste as Tom suggested. If over 30" between centers then we must install a separate drain to each sink via a sanitary tee fitting ONLY(can have single vent here)!

Good day!

Mark