So what is two bucket washing? Simple - you use one bucket with your warm, soapy water, and one bucket as a rinse for your wash mitt. You start with a clean mitt, gently wash the car using both sides of the mitt and after a panel or so you rinse the mitt by dunking it in the rinse bucket, swirling it around a bit and wringing it out. Then (and only then) you put the now-clean mitt in the soapy water again and load it up for cleaning the next panel. If this sounds like "Lather, Rinse, Repeat" from your shampoo bottle, you aren't far off!
So how big a deal is it really? Below are pictures of my wash bucket and rinse bucket after washing the GlossHausmobile, which was dirty, but not "write-wash-me-with-you-finger" dirty (by the way please never do that to anyone: sometimes you'll scratch those words in the paint!!!). As usual, pictures are worth a thousand words (and you can click on them for the full-size view):
The wash bucket: (not bad, right?)
The rinse bucket: (cue terrifying music shower music from Psycho)
I couldn't believe how much stuff was in the rinse bucket! The idea that I was smearing all that junk back on my paint made me an instant believer in Two Bucket Washing.
So what are you avoiding by using two buckets? Simple - swirl marks. Have you ever looked at a car in the sun or bright light and seen this?

By the way, the car above was a collector's BMW 2002 that he kept meticulously clean and washed all the time - he didn't realize he was the source of the swirls. The good news is a little bit of work with the GlossHaus system left it looking like this:
If you have any questions, feel free to post them here, on the GlossHaus Facebook page or e-mail me at lee@glosshaus.com.
Product Notes
You may have noticed the screens in the bottom of the buckets. Grit Guard makes a terrific product that fits in any standard 5 gallon bucket and traps dirt and other contaminants in the bottom of the bucket and away from your wash mitt. I recommend one in each of your two buckets. At $9.95 each, they are cheap insurance. Check out Grit Guard products at our store.
Also, cheap microfiber from big box stores is fine for home cleaning, but will also swirl your car. GlossHaus offers terrific and affordable microfiber products. See the Microfiber selection at our store.
Lastly, you can see the full range of GlossHaus polishes, glaze, waxes and complete kits at The GlossHaus Store at Atlantic Euro