Lemon juice is a natural antiseptic. Baking soda is a foaming agent that will help break down grease and oil. Lots of cleaning products use it. I don't know if that's the specific reasoning behind their use for bud washing though. I don't wash my nugs. I don't use anything that I'm concerned about washing off, but I'm interested in seeing/reading about yours and other people's experiences w the process.
Here's a what I do, I run my buds under lukewarm water right from kitchen faucet, then switch to cold water from faucet, I swirl around a bit to get the nook and crannies. I use medium to light strength water pressure, I don't see the need for 3 buckets and added crap, my way works great for me, take a single bud from next harvest and try it, what have you got to lose? Just remember, light pressure, don't want to knock off those precious trichomes.