Buffalo Evening Times (June 21, 1916), in a list of comic songs:

"Dan, Dan the Lavatory Man."

The Republican (Springfield, Mass,) (May 25, 1925):

"There is a gay and unwashed little song heard in many cities that immortalizes 'Dan, Dan, the lavatory man' Its hero was kindly Dan - [the washroom attendant] of Jack's."   

["Jack's," the popular all-night cafe on Sixth Ave. and 43rd St. in New York City, closed in 1925 after 34 years.]

Narromine [N.S.W.] News and Triangle Advocate (Sept. 16, 1937):

"The refrain of that old classic, 'Dan, Dan, the Lavatory Man,' floated upwards."