My 99 saturn SL2 got regular antifreeze mixed with its dexcool and there is now sludge. I am trying to flush the whole system before everything starts to clog and get ruined. My question is: If there is no radiator cap only a overflow tank how do I properly flush the cooling system with a flush kit? Where will everything flow out of if there is no radiator cap for the dirty water to flow out of? any help would be great

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vertical electric radiators wall mounted