Once you get an O-ring chain, kerosene or diesel is the solvent of choice. Since the O-rings prevent dirt from getting inside the rollers, all you need to do is to clean the outside. More aggressive solvents may get past the O-rings, thinning the grease inside and defeating the purpose of the O-rings...or, even worse, they may actually attack the rubber. Also, soaking an O-ring chain in gear oil just gets the outside oily and only serves to keep it from rusting, which any good wax or Teflon product also does. I used chain wax for years until I found DuPont Chain Saver, which I now use exclusively, about every 100 miles or so. Put the rear wheel up on a crutch jack, wipe chain with kerosene moistened rag, apply Chain Saver, spin chain a couple times with dry rag....done in less than two minutes. Chain stays dry and clean, O-rings stay lubricated. I only clean the chain with a toothbrush and kerosene about every 500 miles now.
I bought a Grunge Brush, but found the bristles too stiff, so reverted to an old toothbrush. Most of my dirt is dust, and the Grunge Brush was designed for mud.