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Location: US, NYC. I am doing a partial renovation of a small kitchen in a 2-family house, and trying to keep the cost down if possible. Plumbing done, cabinets and backsplash installed, countertop and sink are coming soon. At this late stage, I've discovered that NYC recently allowed garbage disposals (I always thought they were illegal), and I'm wondering how feasible it is to add one.

The setup is on the diagram below. Questions:

  • There is an approximately 2 foot long approximately horizontal drain pipe run (usual 1.75 inch PVC) between the vertical drain line and the P-trap. Most of this pipe is behind drywall and cabinets and cannot be realistically changed at this stage. Would a garbage disposal be strong enough to push waste through, or would things get stuck in the horizontal pipe?
  • And what if the pipe is not quite horizontal, but slopes slightly?
  • Are there height restrictions for where the garbage disposal's output should be in relation to the P-trap and the horizontal drain pipe?
  • The P-trap is under the center of the sink, but my sink model drains on the right side. Are there any restrictions on the shape or type of the drain connection from the garbage disposal to the P-trap?
  • There is no dedicated switchable electric outlet under the counter for a garbage disposal, so I thought of plugging a wireless garbage disposal switch into the same double outlet as the dishwasher. Bad idea? Otherwise, the wiring job would be a bit complicated and would require breaking the backsplash.
  • Generally, does anyone have experience with garbage disposals in NYC?

The setup

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  • Disposers are not worth the trouble and expense. Many municipalities discourage the installation of disposers because of the extra load on the municipal sewer treatment service. – Jim Stewart May 11 at 21:38
  • Have you located what you would use as a source of power for the disposer? Installing the garbage disposal itself is fairly trivially easy, but if there isn't a suitable circuit already present, you likely need an electrician. If the area below is unfinished, you may be able to do it with a homeowner's permit instead. You should check the height of the drain pipe coming from the wall so you know how high the outlet of the disposal unit needs to be. – K H May 12 at 3:32
  • @K H, what would make a circuit suitable? I was planning to use the dishwasher power outlet located in the cabinet to the right of the sink. That outlet is not switch-controlled, but I thought that a wireless switch kit designed for garbage disposals would work. – nyc_relative_newbie May 12 at 5:39
  • One of your questions is about the disposal "pushing" waste through the plumbing. That horizontal bit of pipe should have a slight slope away from the drain. 1/4" per foot of run is the standard. This is what prevents water or other waste from settling in the pipe. The disposal doesn't "push" anything. It just grinds solids so they'll float in the water. It's always recommended to run additional water after you turn off the disposal to ensure that ground solids are washed down the pipes instead of sitting in the disposal and/or any horizontal runs. – FreeMan May 12 at 13:23
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Prompted by K H's comment, I've looked at the specs of my dishwasher model and garbage disposal, and the sum of their current draw is over 15 A. Not a good idea to plug that into one 15 A circuit.

So irrespective of plumbing questions, a garbage disposal would require adding a new electric circuit in the kitchen, which would be too expensive given my planned renovation budget.

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  • One question: is the existing circuit wired in conduit, or was it done in cable (BX/AC or MC)? – ThreePhaseEel May 12 at 23:43
  • I have no idea what's in the ceiling, but the outlets in the wall are on BX. – nyc_relative_newbie May 13 at 13:02

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