Can the kitchen sink waste pipe run from where it comes out of the concrete slab to the sink by running horizontally under the cabinet floor

drainfloorsinkslab

We are converting a peninsula into an island and need to move the kitchen sink. As a result the waste pipe in the concrete slab comes out in the front (see photos) instead of the back. We don't want to jackhammer the slab (I think HOA forbids it) but I wondered if we could come out of the slab with a 90 degree elbow, run under the cabinet floor so and come out in the back of the cabinet where it used to be, or even in the hollow wall we have built behind the cabinets. Also we need to replace the floor of the sink cabinet so we could even raise the floor a little higher.

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Best Answer

Horizontal - no.

No drain line is EVER horizontal. Unless someone was an idiot and should not have been plumbing....

Perfectly acceptable to run at an appropriate slope, however. 1/4" per foot (or 2%) is the standard minimum slope for small drain lines like this.

How will you handle the venting? That is a complex process for island sinks, and if it was a peninsula before probably not arranged for. You mention having a "wall behind" - can your vent run through that (is your island not an island in the usual sense?)

There are ways far less drastic than a jackhammer to get into concrete and rearrange plumbing.

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