Hi Gary, Never heard it. As it stands, it would mean "using" vs. " Are you thinking of dish soap, or liquid body soap, or mechanics' hand soap?
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Ah, then it's British. It's that thick detergent you dilute with water and use (generally with a sponge) to wash dishes, cutlery, pans etc.
Actually this is not my sentence. It is a sentence from the Cambridge dictionary and I post that question to learn the meaning of "washing-up liquid"