Green’s Dictionary of Slang

(US) washday.

1859		Matsell Vocabulum.
1954		Star Phoenix (Saskatoon, Saskatchewan) 11 Sept. 8/7: [advert] Mrs Housewife Have You Got a Bulky Bundle of Suds-Day Blues?
1966		Province (Vancouver, BC) 19 Dec. 4/6: ‘Why don’t you invent something gayer, along the lines of ‘the fountain will play every day but never on Suds-Day’?
1971		Tampa Bay Times (St Petersburg, FL) 8 Apr. 6/5: [headline] Suds-Day Morning Counting Down.