Check out my thread "Accumulator's Non-marring Wash Technique" in the Hall of Fame Forum. IIRC the info you're after is on the second page.
Generally, the idea is to spray the foamgun output at the point where the wash medium contacts the paint so it can provide constant lubrication and flushing- "dislodge and flush".
With a BHB the foamgun will keep things rinsed pretty clean, but with a mitt I'd rinse it out numerous times per panel; once dirt is stuck to the mitt it can cause marring.
When I get my technique right, my rinse bucket hardly has *any* dirt in it even at the end of a winter-nasty wash. This tells me that the dirt wasn't stuck to my wash media, which could have caused marring when it got moved across the paint. I have to use a BHB for the initial pass(es) as it does the "dislodge and flush" thing a lot better than a mitt will. Even after doing the initial pass(es) with the BHB, I rinse my mitt out quite often; I never go a whole panel before I rinse it out.