Not one to spend money on an item I may have around the house, I decided to try a spring in a jar for a brush cleaner (based on that coil cleaner thingy sold by Blick). It works great! Any hardware store carries springs and you'll want one with thick coils about 1/8" apart. Measure the inside diameter of your jar, so you can pick one that doesn't move around much so you don't stir up the bottom sludge any more than necessary. Fit that into a jar with a nice wide mouth, and you have an easy to clean and effective brush cleaner. I top it off to about 1/2 inch above the spring once a week.
When the sludge builds up in the bottom, pour off the clean OMS on the top, into another wide mouth jar, use a pair of needle nose pliers to squeeze the middle of the spring (if it's snug) and slip it out onto a paper towel. A quick wipe of the spring, use the piece of paper towel to scrub out the sludge at the bottom, pop the spring back in, pour your OMS back in and you're good until the next cleaning is needed.
When the sludge builds up in the bottom, pour off the clean OMS on the top, into another wide mouth jar, use a pair of needle nose pliers to squeeze the middle of the spring (if it's snug) and slip it out onto a paper towel. A quick wipe of the spring, use the piece of paper towel to scrub out the sludge at the bottom, pop the spring back in, pour your OMS back in and you're good until the next cleaning is needed.