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I've got no experience with plumbing, but I'm trying to learn. We've just bought a new home and are preparing to redo the kitchen, which is... delightfully old. We want to add a dishwasher where the sink is currently, and move the sink over to the window.

I'm not sure, once we move that sink, what our options are for draining: is it more reasonable to run new pipes through the floor, or should we try to stay along the back of the cabinets in empty/blind space mostly to the old pipes? Do I need to consider new venting?

As a side-question, does the dishwasher HAVE to drain into the garbage disposal on the sink, or since the old drains for the sink are right where we're putting the dishwasher, can we just route it into there? I assume we'll need a p-trap.

Sink and kitchen currently Detail on cabinets

Beneath the new location for the sink, we have a basement door so we can't go below the joists - if we REALLY have to, we can sacrifice an inch or two but we're planning on finishing the basement and need the ceiling height.

Under new sink location

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Judging from the stack we can see in the last picture it looks like your drain and vent are in the wall behind the existing sink location. That is certainly where they would be expected given it's probably all original.

Putting any new drains or vents in the new locations, given the window, door, and direction of the joists, will be challenging. Not impossible, but there is no need to create and solve these problems. The easiest way is to run the drain pipe on the surface of the wall, behind the cabinets or drawers, to the existing location or nearby, ideally perhaps in the corner, where you can go through the floor into the joist bay where the drain stack is.

For venting you'll open the kitchen wall up behind the existing sink location and connect the new drain (coming from the window area) to the vent stack somewhere .... perhaps higher than the existing drain.

Your dishwasher doesn't have to drain through the disposal but there's no reason not to in this situation. Just run its drain hose around the corner to the new disposal.

You may change the details but the essential thing about this approach is to hide some new pipe work behind cabinets so that you don't need to go through studs or joists and also don't need to build a new drain stack.

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