How do I clean the brush after painting? How do I wash it? Can I wash it in the sink? Probably not cause sink will be tainted with the paint. Basically, practically speaking how do you clean the brush after painting?
First I "paint out" the brush (try to paint scrap material, cardboard etc.) until the brush is too dry to paint. Then:
Assuming I have flowing tap water on site, I rinse the brush with lots of water, we're talking gallons. Then when most of the paint is out of it, I start working in whichever hand or dish soap is convenient, both the clean the brush, and also my hands, and also the sink. Fair play to use the brush to clean the sink. Then I thoroughly rinse all the soap out. Then I hang the brush.
Oil based (alkyd, enamel, varnish etc.)
First, do I expect to continue painting in the next few days? If so, I wrap the brush tightly in plastic, and double wrap it.
I put 10mm of paint thinner into a soup can, and momentarily dip the brush just to re-wet it, and repeat the "paint out" procedure above. Several times, until it seems like a lost cause. Then I mash the brush around in the thinner, working the thinner throughout the brush especially the heel (where the bristles go into the ferrule). You do not want paint accumulation there. If there's a safe space to splatter, I whip the brush around to use centrifugal force to throw thinner out of it.
If I want it really clean, I get a clean can and put 5mm of thinner in the bottom and repeat the above. Then I hang up the brush to dry.
2-part epoxy and urethane "paints"
I wrap the brush in plastic, and throw it in the trash.
Why? Simple rule: Don't spend $5 in thinner to clean a $3 brush. Epoxy and urethane reducers tend to cost a fortune. If you don't pay for the reducer, ask the person who does.
For throwaway brushes I like Redtree Fooler brand, they are a cut above, and sanely priced if you buy wisely.
If I expect to continue painting in the next few days, I will wrap the brush in plastic and throw it in the freezer (a dedicated fridge for this purpose).
When I say "hang the brush" I mean dangle it by its hole in the handle, on a nail, hook or wire, over somewhere where dripping won't do harm. That way the bristles dry straight.