The soap scum would probably clog the drain after a while. You would have to definitely use something with no superfat or even a little excess lye. If you have hard water, you'd also probably have to chelate in order to prevent scum from getting all over your dishes. I haven't tried it, and maybe there's a way to make it work, but when I wash my soap dishes in the dishwasher, even after a preliminary hand washing, I tend to get gross dishes unless I throw in a splash of tetrasodium EDTA in the final rinse cycle. Granted, I use a 5% superfat so that could be the main cause.