I hope I can get some answers before I have to spend more money! I'm in the process of buying a new dishwasher because the motor pump is leaking and cannot be reapired (only 5 yrs old)....
The main problem is that the sink is backing up to the dishwasher and also the sink drains very very slow. It only works when I turn on the food disposal, which by the way also has an on/off leak.

So, I need to resolve 3 things:
1. Water drains very slow and have to use food disposal for draining it.
2. Water backs up to dishwasher
3. Food disposal leaks on and off.

Any help will be greatly appreciated,
Sandra

If the diswasher is draining into the disposal on the side of it where they provide a connection to the washer, your issue is with the disposal as its partly plugged with stuff.
If the disposal drains properly with the faucet and not being turned on that indicates to me that the plug knock out that is provided in the disposal may not be all the way out and is partly plugging the drain.

The reason that the water backs up into the disposal is that the hose discharge is below the drain connection. The hose should run up over the height of the washer and should be connected to a air gap device to prevent the water from being sucked out of the machine. Both required by plumbing code.

If the disposal is leaking it sounds like either the person installing it did not do it correctly and has no understanding of plumbing as it appears that both the dishwaher and disposal is giving you problems. I expect the leak your talking about is in the area of where the disposer connects to the sink? If so the metal tab ring that locks the unit onto the sink is most likly not properly fastened. Other then that there should be no leaks anywhere else. If so, disonnect the power to the unit until it can be checked out.

Thanks for your promt reply. I raised the hose discharge above the disposal and after I did some dishes yesterday, no water went into the dishwasher. So that might be taken care of.

I have to look carefully with a flashlight, but it seemed that the leak on the food disposal was from the bottom of it, and not on any connections. Is there a fix for that?

Lastly, can you give me a possible diagnosis for why the sink does not drain unless I turn on the food disposal. It does drain very very slow, but it will fill up and I have to start up the disposal to get rid of the water. I tried Drano but it did not work. Thanks in advance and Happy New Year!

The disposal may be plugged with partials of old food stuff. It sounds like your in need of a new disposal. If it appears to be leaking from the bottom the seal is damaged and quite frankly although it can be fixed, it will end up costing as much as a new disposal would.
I would replace the unit with a new one and you will most likely find both the leak and the issue with the dishwasher will go away.
do not forget to intsll the air breaker device or integral backflow device on the hose from the dishwasher to disposal unit. It connects in the middle of the hose at its highest point. What it does is prevent the water that leaves the dishwasher from siphoning all the water out of the unit. It is required by the IRC and UPC codes.
It should cost you about 10 to 15 dollars for the device.

Great! THanks so much. I was leaning towards getting a new disposal too. I also asked someone last night at a local store and they suggested the same thing. I appreciate all the valuable information and guidance.
Sandra