You may or may not be able to get this cheaply, but I had some industrial ethanol laying around - 99.5%, I think? Anyway, the DG 105 I had on a black foam pad was soo tenacious in my APC wash solution; if you pinched the foam and squeezed outward, you could collect tons of residual sealant, still in liquid form. Then I got the idea, and tossed the pad into my bathroom sink and saturated the pad with ethanol and some more to boot, so that the "dirt" had somewhere to go instead of staying inside the pad. The ethanol instantly turned yellow and the pad turned to pure black again.
Sweet.
Sweet.