The phrase "soapy rag" refers to a cloth or towel that has been dipped in soapy water. It is commonly used for cleaning and scrubbing surfaces. Full definition
Next, I took a warm soapy rag and scrubbed the stool clean and free of cobwebs. (purelykatie.com)
their Textured basecoats are amazing over crazy surfaces like metal, laminate floors, ceramic tiles, glaze etc etc — this paint will stay put, EVEN without being sealed, it just requires your surface be soapy rag clean, wax free, and dry. (fabulousfinishes.wordpress.com)
If your image has smeared, you have a few minutes before it dries so that you can remove it from the surface with a wet soapy rag. (inmyownstyle.com)