Buy a brush spinner and a brush comb. The spinner runs about $15, the comb $2.
the spinner looks like a smal bicye pump. You push the brush's handle into the bottom of the spinner, hold it in a drywall bucket 9or equivalent) then pump the top. this spins the brush at a pretty good pace, and the spinning removes virtualy all contaminants from the brush. I usually spin the brush 3 times, rinsing in solvent (either spirits or water) between each spin.
After spinning, comb the bristles then store as Mr. Paint described.
I have two coffee cans with mineral spirits in them. The first can is for the first dip and swish. Then I spin. Then I dip and swish in the second can. Then I spin. Then I usually poor a small amount of spirits right out of the can and on to the bristles. Then I spin again. The brush is as good as new.
Comb and store.
I cap the coffee cans and by the time I use them next, the solids have settled to the bottom of the can and the sirits are again clear and ready for another cleaning session.
After a lot of painting, I'll end up with a few inches of solids on the bottom of the can. Time to get a new can.
Don't ever pour mineral spirits down the drain. Set them outside and let them evaporate, then toss the left-behind solids with the trash.
If yo have paint to dispose of, remove the lid and set the can outside. The solvent will evaporate, leaving the solids behind. Let it harden then dispose of it.
When using $25-$40 brushes, a $15 spinner is well worth it. Properly cared for quality brushes will last a DIYer a lifetime.