[JimD]

When I bleed brakes or flush out old brake fluid, I do not put the new fluid in the container of the brake bleeder. It wastes fluid, give the air more surface area of the fluid to try and work moisture in, and it creates more work by creating a need to clean the container. Instead, I refill the brake reservoir every wheel or two. It is really bad to let it go dry (you will then inject air in the lines) but this doesn't happen unless you don't check it. It is a bit of a pain to take the cap off the reservoir to put in new fluid but it is a bigger pain to clean the big bleeder reservoir. If you leave old fluid in the reservoir, you will start your next job at least potentially putting in worse fluid than you are replacing - moisture pickup is a big part of why you need to replace the fluid in the first place.

Jim