1. 2 min is sufficient, given the water circulates on the print surface. Sitting in a stagnant water doesn't count. A stack of prints with no separation doesn't work either. But other than that 2 min is good.
2. How you circulate the water is not that important. You can fill the tray, rock the tray frequently, change water every 30-45 sec., and repeat the process for 3-4 times and the print will be ready. Siphon, hose, whatever that fits your tray, sink and technique. I use extra large (30-some inches) tray and L-shaped PVC pipe with lots of holes to wash my prints.