As long as the line is sized and installed correctly you should not have any problems.

Quote;"As long as the line is sized and installed correctly you should not have any problems."

That is a rather arbitrary statement and may not be true.

Under both the IRC and UPC the maximum allowable length of a fixture drain arm is very finitely regulated by code.

Before we could offer an answer we would need to know where the vent line connects to the drain line behind the wall.

We also need to know the diameter of the drain line.

Under the IRC a kitchen sink is rated at 2dfu's and is required to be connected to an 1-1/2" P-Trap and drain line which may run a maximum of 6' from the trap weir to the vent opening.

If you are under the UPC it gets a bit tricky to figure. Under the UPC a kitchen sink is also rated at 2dfu's and prior to the late 80's the code required an 1-1/2" P-trap and drain line which could run a maximum of 3'6" from the trap weir to the vent opening.

In the late 80's the UPC de-rated and 1-1/2" line to a maximum of 1dfu. The UPC now allows either an 1-1/2" or a 2" P-Trap but the drain line is now required to be a 2" line, which is rated for up to 8dfu's on a horizontal run and a 2" fixture arm is permitted to run a maximum of 5' from the trap weir to the vent opening.

Now be careful here. If your under the UPC and your existing sink was installed before the change in the late 80's it probably has an 1-1/2" drain line but if you move the location of the sink that is technically defined as "New Work" and you are required to conform to the code that is in effect at the time of the new work, which means if you move that sink you would be required to change the entire fixture arm to 2".

Also, Under both the IRC & UPC if you are connecting to the existing fixture arm and running a horizontal line through the cabinet you would be required to install a Wye & 1/8 bend on the fixture arm with the new horizontal line connected to the side opening and the top of the wye would have to be fitted with a thread adapter and a screw in cap as a cleanout.

Thanks for the truly helpful responses! I kind of liked the first one, but the second response definitely gives food for thought. The drain line is 1-1/2" and we are in a UPC jurisdiction. So what I take from this is that I could install a new sink in the same location without changing the pipes, but if I move it, I run the risk of an inspector coming in some day and challenging the setup if I choose to keep the 1-1/2" drain (which works great right now). Let's assume I'm willing to run that risk. What I would like to know, lazypup, is this: does adding length to the horizontal run make a difference in function; i.e., should I be more worried about using a larger drain pipe if I add to the length of the horizontal run?

I don't know how to locate where the drain line runs into the vent. I can trace it down to the basement, but it's not obvious to me where the venting happens. It looks like there's one main drain pipe with an associated vent for the toilets, but the vent for the sink drains isn't so obvious. I also need to research what a "wye" is... I suppose my ignorance would suggest that I should just hire a plumber before I ask my brother to install this sink. But gosh, it would be nice to save that money! Thanks for you help; although it confuses me in a way, it's always good to know there's more to the problem than I was otherwise aware of.

"That is a rather arbitrary statement and may not be true. "

As you clearly explained it can be accomplished under either of the model codes.

That would mean if it complies it should work just fine.

Important note to kmcg, and other readers: trap arm sizing is a subject that some Master Plumbers get wrong. Double check before you upsize. On the subject of trap arms, I've spent hours refuting our resident expert internet plumber. If someone writes that you need to go bigger, don't take their word for it. On other discussion forums, inhabited by Master Plumbers, you will read different advice. Hmmm.

On a situation like this why not go to the source, it will only take a phone call to the plumbing inspector and he will definitely tell you what you can and can not do. A lot of master plumbers have their own interpretation and definition of the rules. The inspector is the final word, go by what he says.

"it will only take a phone call to the plumbing inspector and he will definitely tell you what you can and can not do."

The AHJ is not an advice service.

They may try to answer (but are not required to) but cannot be held to the reply.