Green’s Dictionary of Slang

(US) a radio or TV serial drama, a synon. for soap opera n.

1942		Life 27 Apr. 72: Soap operas [...] are 15-minute daytime serials aimed at housewives. Some people call them ‘washboard weepers’.
1949		N.Y. Times Film Reviews 2451/2: Why not combine the lushest features of a video variety show with the sentiment of a washboard weeper? ‘I’ll buy it!’ somebody must have cried.
1959		Sponsor XIII:2 12/2: They started talking tough [...] about ‘cliffhangers, washboard weepers and soap operas’ .
1962		I. Robb Don’t Just Stand There 200: It is a real washboard weeper, a tale of heartbreaking struggle, hand-to-hand combat and constant defeat in my unceasing efforts to persuade, cajole, plead, threaten and bribe the countless laundries of New York City.
1970		N.Y. Times Bk Review II 70: A woman whose washboard weepers were the joy of many a housewife — but whose own life was far from sudsy white.
1983		D. McCall Bluebird Canyon 234: Rex thinks he's so fucking important. And it's nothing but a dumb soap opera. It's not dumb. Poor David. A Washboard Weeper.
2002		J. Cox Say Goodnight, Gracie 143: Charles Eagleton, playing Ma’s confidant and business partner Shuffle Shober, was with the washboard weeper for 25 years.