this has been covered many times (search), but dawn power dissolver (available at walmart for around $3 a bottle) does an excellent job. spray on the pad, let it sit for 10-15 minutes, massage product out of pad under running water, squeeze/swing out any leftover water, lay on grit guard to dry...
I usually let the pads sit in hot water with whatever dishwashing liquid I have on hand. That seems to do the job for most applications. For heavy duty removal of stubborn caked on materials, nothing is as easy to use and effective as dawn power dissolver.
Dawn or Simple Green in a bucket with hot water. I let it sit for a few hours. Rinse thoroughly and dry in a covered place. I use to wash them in the machine. But the backing would peel off after so many washes.
I had cleaned a couple of pads with some dawn detergent and after they were dry, I was just not sure if I got all of the product out of the pad. They seemed a little rough on the surface, although I can't really see any residue. Would it be best to just pitch them or maybe soak them in a bucket with some water/DP pad restorer?