If you intend to just do a drain and fill it is fine. Whether the drain plug is dirty is moot as there is nothing you can do about it except clean the plug. Unless you know it is the lower hose that pushes the transmission fluid out into the radiator I recommend you pull the upper and lower transmission hoses. Attach the clear hoses snugly over the metal part of the transmission hoses that comes from the transmission. The fluid in the radiator will drain out so get ready to catch it.
The instructions are good in this video.
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