When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Drain the radiator into a clean container. R & R your hoses and valve. Put the antifreeze back in when you're done. Strain the barnacles and fish heads out of the used fluid with cheesecloth or something like that. A coffee filter is too fine- it won't pour through very well.
You could lightly clamp the 2 hoses to stop coolant loss for a fast switch. If you are wanting to change coolant anyhow now is the time.
Prepare to catch some even if you drain the radiator.