I think the plumber will have to lower the waste drain in order for the disposal to empty fully. That means cutting a hole in the back of the sink cabinet then cutting a hole in the drywall to get to the waste pipe which is then cut lower. The dry wall is replaced and then the garbage disposal reconnected to the newly lowered waste drain. It is an expensive process.

You can NOT have a sink connected to a drain without a P trap. The P trap stays full of water and thereby keeps the sewer gasses out of your house. That's good on an odor front, and because sewer gasses can build up and either kill you from just being present and from exploding, as they are flammable. You need to get a licensed plumber out there to redo the waste arm going from the P trap into your wall where it connects to your drain. (No TRUE licensed plumber would EVER suggest removing a P trap! It's way too dangerous and that's why it's against code.) Redoing the waste arm is more expensive to have done than just installing a disposal, but not that expensive compared to dying!

Oy! Live_wire_oak, you have me freaked out! I'm pretty sure the plumber that came by was a real plumber.

If the water is staying in the garburator, can it be functioning like a p trap?

I think I need a Holmes inspection!

Unfortunately for an easy solution to this problem, the IPC limits how far down one can drop the waste to a P-trap, usually precluding putting it in the basement. And moving its interface with the drain pipe in the wall depends on where the vent actually rises relative to the drain connection. Much ravaging of the wall may be needed in some cases.

There is some variation among disposals such that some may give you more room than others. That is, the distance from the sink to the drain exit varies. A new disposal may be less expensive than moving the plumbing in the wall. The ISE Evolution series may be helpful in this context.

kas

My franke sink is 12" deep. We have an insinkerator 1hp and had no issues what so ever. perhaps you need to try a new brand????

I just ran into this problem yesterday - I'm doing a gut rehab of my kitchen (now about 95% done), and I'm using an undermount sink that's 9" deep on one side, 7" deep on the other. I wanted the disposal on the deeper side of the sink, but since I didn't plan for that from the beginning of the rehab, the plumbing (which was totally redone) came in at a standard height, came through the cabinet at a standard height, and then wasn't low enough to allow the disposal to drain properly from the big bowl. So, to my chagrin, the disposal is on the small bowl. I thought about a lot of things before the reno, but i never thought of this! So, a word to the wise: if you want a deep sink, plan ahead on the plumbing.

This isn't rocket science, the only thing a plumber has to remember is that s**** should always flow down hill. This means that the garbage disposal's drain outlet must be higher, usually about an inch, than the drain going through the wall. This was never much of a problem until deep under-mount sinks came into the picture. A 9" deep under- mount sink can drop a standard size disposal nearly 2" inches, often resulting in it not being able to fully drain. Cheaper than ripping out the plumbing, one solution is to purchase a compact model disposal. Not as deep, these often have the waste outlet high enough so as to eliminate this problem. Check the specifications and dimensions carefully.