How do you wash brushes?
When using mineral spirits(MS), I keep a "used" bottle and a new bottle. When the new is empty, I make it a new "used"

I usually do the first round using used MS and return it to the used bottle.

Once the brush is mostly clean, I start using fresh, clean MS.  I usually do 2 rounds or more, if paint is still  coming out

I don't do a water/soap step until I'm sure it clean.  If I'm using a china bristle brush (natural white or black boar bristles), I NEVER use water with it.

If a brush has accumulated gunk and isn't getting clean, a soak in a "Brush cleaner" product will restore it.

PS:
The used bottle, if left undisturbed long enough (2 mos) will self-clean and be nearly new (the solids will settle on the bottom).  This then argues for a third container, between new and used.  You should NEVER put MS down the drain.