You don't use WD40/GT85 on chains.
black messy chains = too much lubication.
GT85 is actually pretty good at cleaning chains: spray it liberally on a cloth, clean chain then apply lubricant of your choice.
I usually spray degreaser to removed the murk off before applying lubication.
@Jon. started
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You don't use WD40/GT85 on chains.
black messy chains = too much lubication.