This is ads about lye (https://en.wikipedia.org/wiki/Lye), an stuff that help you make soap. So, back in those day, people make soap at home to save cost, not because they want 'homemade' soap.
"Grease" in the ads was fat from animal. People have ton of those because they live in the farm. Grease is one of by-product of butchering animal. The 'lye' is something that help turn grease into helpful stuff (soap) and save cost.
Clean as in strained to remove particulates