Possible Clues:

• I can't remember drinking that!
• Allow the man to show forgetfulness
• "Whom, on the wharf of –– waiting, / Count you to find?" (Housman)
• Allow him to be ungrammatically forgetful
• Flower, certainly not related to forget-me-not
• Oblivion; river of the underworld
• In Greek myth, the river of forgetfulness
• Ethel's mythical river of forgetfulness
• Where the hades can one get so absent-minded or allow the man to be like a river
• River where elephants never drink?