you shouldn't tip white spirit into any drain, nor paint.
the easy thing is to use brush cleaner, the blue stuff sold in paint shops. Wipe off as much as possible of the paint from your brush onto newspaper which you can throw away, work the brush in the cleaner to get it well into the bristles and stock, leave it while you have your tea, then work it through again, wipe off as much as you can, then rinse out several times in fresh water.
Use a glass jar not a plastic container.
If you screw the lid on tight and leave it for next time, the paint residue will sink to the bottom and you can pour the cleared brush cleaner off into a new jar. Never mix water with it.
If you are doing a lot of oil painting, a surprising tip is that if you throw the brushes in jar of paraffin, it loosens the paint and it easily falls out of the bristles. Again, you can leave it to settle and re-use. Of course you have to clean out the paraffin later, you can do this with detergent or with brush cleaner, or you could use white spirit if you don't mind the expense. Paraffin gets paint out faster than white spirit or brush cleaner and is cheap.
The trouble with white spirit is that it just dilutes the paint, so there is always some left in the brush.
Keep separate brushes for White and for Colours as slight colour residues will tint your white paint next time (true).
Some paints will wash out with water and a little washing-up liquid. look at the label.
Avoid cheap thin brushes. A good brush, well-used and well-cleaned, paints better than a new one.
