BlkYukon- Good video!
Perm- I'm among those who spend *more* time with the foamgun and consider it a tool for reducing marring more than a tool to save time. But you can still do that too:
As per blkyukon's video, rinse, presoak, then wash.
I'd do the washing *little* differently, long explanation follows:
The general idea is to "dislodge and flush away" the dirt.
I'd use a BHB (especially if you're trying to save time), which will free-rinse pretty well if you blast the foam at the point where the bristles touch the paint. When I rinse my BHB out the rinse bucket hardly gets *any* dirt in it, so if you really want to save time you can do some pretty large areas without stopping to rinse the BHB at all. I can't get this sort of free-rinsing with a mitt, though shooting foam from inside a MF/chenille mitt (the "mitt balloon" technique) is sorta similar.
I just "jiggle" the BHB/mitt instead of making wipe/long passes. That way if I get any marring it'll be short, little scratches and a 1/4" scratch isn't as bad as an inch long one (let alone a really *long* one).
I move the foamgun so that it sprays suds along the full length of the BHB, really close so that the suds hit with some force- this does the flushing. This takes a little practice (rub head/pat stomach type of thing) especially if you're jiggling the BHB while you move it across the panel. You really do need to keep the whole contact-area of the brush well flushed.
Gotta watch that you don't bump the panels with the foamgun's bottle or the hose when you do the horizontal surfaces, this makes it tricky to keep the suds right at the point of contact. I usually have the hose over my shoulder the way I do with the cord of a polisher and I hold the foamgun at an angle (which works OK if the bottle's full).
The process of spraying foam right where the bristles touch the paint, holding the BHB so that you barely touch the paint (just enough to barely bend the tips of the bristles), jiggling the BHB while moving it across the panel, and moving the foamgun to spray along the full length of the BHB sure isn't easy! For vertical surfaces, I rotate the foaming nozzle of the foamgun so it sprays vertically.
Instead of rinsing in a bucket, you can just spray the BHB out with the foamgun. Not as good as dunking it, but we're trying to save time, right? Again, if you do the washing right it'll pretty well rinse itself out, all the dirt will get flushed away.
This is the best combination/trade-off of speed, lack of marring, and effective cleaning I've found yet.