Apparently the garbage disposal drain must be above the drain stub, but I can't find a clear answer for how much height difference is actually required.
Let's use this drawing:
The question is how much higher does the disposal drain (#1) have to be relative to the drain stub (#5)? I've seen answers ranging from "just above it", to 1 inch, to 4 inches, so what's the actual minimum I can get away with?
Also, how do you measure it? Is the important measurement going from the bottom of #1 to the bottom of #5? Or from the bottom of #1 to the top of #5?
Best Answer
I don't think there's a code imposed minimum, but there's likely a physical limitation based on available fittings.
Between the disposal outlet and the drain, there must be a trap. The bottom of the disposal outlet, must be above the trap weir (the point in the trap at which water starts to drain from the trap).
Therefore, in theory the bottom of the outlet has to be just slightly above the bottom of the drain.
In reality you'll have to use available fittings, so the minimum height would be based on what the fittings physically take up. Bare minimum, you'd exit the disposal with a 90° elbow, and connect directly to the top of the P-trap. So whatever height is taken up by the elbow and P-trap, would be the minimum.