Water base: 3 gal water in a 5 gal bucket. Paint brushes really shouldn't be loaded more than 3/4 of the way up the bristles. Metal ferule should not be covered in paint. For a good finish on larger jobs, clean your brush every 30-45 minutes. Stick in in the water and "comb" the bristles with a wire brush. until it looks fairly clean. A bronze grill-cleaner wire brush works well, won't rust, and is cheap. Reason to clean so often is build up in upper portions of bristle will start to thicken and dry, reducing ability to evenly load the brush and possibly shedding into your wet edge. If you are not going to use the brush for over a 30 minute period, comb it out in the water bucket, tap it "dry" on the edge of the bucket then wrap tightly in a recycled plastic bag from the supermarket. You can leave a brush like this for a couple of days, but its not good for it. I have "good" brushes ($30-$50) that I have been using for close to a decade with proper care. If you have never used a good brush vs a "big-box" $10 special... Try it. You will be amazed at how much easier it makes the job. You will never go back, as long as you look after your investment.
Oil base finishes is about the same, but use the proper solvent to clean the brush. In either case, when you think the brush is clean, comb it out one more time, then a quick wash with some mild detergent, comb and let dry. Proper cleaning will probably take 10 minutes total plus the walk up the hill to the spigot. You will thank yourself tomorrow.
For staining, I usually use cotton painters rags or muslin for application and wipe off. No cleaning required. Stain rag can be left in the bucket or hung out to dry. Do not store solvent based stain rags that are not dry or in the stain can. Spontaneous combustion is real.
The plastic bag trick can be used for rollers as well on roll and tip jobs. No need to remove roller from frame, just make sure bag is wrapped tight around the handle. Quick and dirty latex jobs good for up to 48 hours with double bag. High end work, stash it in a single bag while you do lunch.
Thanks folks. Good thoughts. Yes I have latex and oil based cleaning challenges. Had a less than perfect latex paint outcome today as a result of using poorly cleaned brush. Oh well will sand smooth tomorrow and do right.
Cling wrap will keep the brush soft and pliable with most products as long as they are not chemically activated (two-part). With water based products and varnish I have kept brushes and rollers alive for literally months when properly wrapped in cling wrap (all air removed).
Also as long as the brush/roller is not a really expensive one, I've discovered that it is often more expensive to clean than it is to replace.