Back on the farm I remember Joel and I used to clean our bikes and chains using kerosene. We'd tap off a washbowl of kerosene from the tank for the chick heaters, take the chains off the bikes, then scroll them through the kerosene scrubbing with cleaning brushes and rags as we went. Finally drip some chain oil (I think we used sewing machine oil) on as we rolled them back onto the cogs, and wipe the bike frame with the cleanest part of a kerosene-damp rag. This was waaaay back when we still had chickens and lived at the old house. I can't have been 10 yet, Joel no more than 12. I have no idea why your grandparents let us use flammable liquids with no supervision (or maybe they were watching carefully and we just didn't notice). We did have a specific place for the flammable rags afterwards! Anyway, you're a grownup now so you could certainly do this safely on your own. Also there are chain cleaning fluids that might work better, though they're likely to be more expensive. And I think you're right that since you're riding in rain and mud, it can't do all that much damage to use water as long as you dry and oil the bike well right away.