My drain pipe sits 19-19.5" above the floor--pretty high. I am hoping to install a deep under mount sink but I know that my disposal outlet pipe needs to be above the main drain. I have done the math (we have 38" cabinets and I bought a disposal with the outlet pipe only 6" below the sink) and it will sit @ 20.5" above the ground--about 1" above the main drain. Is this adequate slope to keep the disposal draining properly? Does the minimum of .25"/ft slope apply to this as well? I can't find any information about how much higher the disposal outlet should be, only that it should be higher...

Hello Rkmanna,

I suggest to take a picture of your disposal and the pipes connection that the expert on this site will see it and give you there advises, also open the link below you may get an idea, Thanks.

John

plumbing - Help with Garbage Disposal install and high drain pipe - Home Improvement Stack Exchange

Put a trap and trap arm on the disposal. Put the rubber mounting gasket of the disposal on the disposal. Measure the distance from the top of the disposal gasket to the center of the trap arm. Add 1/2". Add that measurement to the depth of the sink. That will be the maximum height of the drain when measured down from the top surface of the counter top.

" Is this adequate slope to keep the disposal draining properly" yes.