i bought a chain cleaning tool from the shop.

I've heard recommendations of 200 miles. I'm running at more along the lines of 400-800. rain brings things to an immediate head, though.

here's how I do it:
better if one has a stand, but I have flipped my bike upside down. Using the tool makes it easier, and i direct the hose (medium flow) at the rear cog and "output" area of the tool. the water picks out the grease and degreaser and pretty soon the chain is nice and shiny. then i remove the rear wheel and spray the cogs and using a clean towel edge I insert it and pull it to the right (the set turns) for a partial turn, then to the left (it stays) and continue the process, respraying (simple green in my case) as needed. Usually only one circle is needed to get the gunk off between each ring. Then i hit the rings up front. If you only get it off the chain, you only get half the problem cleaned up.

I return the wheel, run the chain through a few spins against a dry towel, and reapply oil according to directions.

i hope this made somewhat of sense.