Sorry if everyone knows this already. I've always used MF towels with ONR, lately it's been the Cobra 530 Supreme. Well, I tried a grout sponge from Home Depot today. Boy, that sponge really trapped a lot of dirt. After my wash, I rinsed the sponge in about 2 gal of clean water in a white bucket, squeezing it every which way. I tell ya, that water turned murky gray in seconds, but happy to say, there was no solid grit at the bottom. I had to rinse it a couple more times after that until the water was clear. Wow, so that's where most of the dirt goes (or at least the non-marring type of dirt)!!
This is how my ONR solution looked after washing a week's worth of dirt on my daily driver with the HD GS (but before washing the wheels):
I started with clean water and then rinse the GS and this is how the bucket looked like. Note this trapped dirt was only from the panels, I didn't wash the wheels with the sponge:
This is how my ONR solution looked after washing a week's worth of dirt on my daily driver with the HD GS (but before washing the wheels):

I started with clean water and then rinse the GS and this is how the bucket looked like. Note this trapped dirt was only from the panels, I didn't wash the wheels with the sponge:
