Possible Clues:

• Overwhelm single sister with romantic assignment
• Cover with water
• Flood — and unite (anag)
• Overwhelm (as if) with water
• You monk, but ___ (time to get fully immersed)
• Submerge
• Flood means Aunt Enid has to move
• I make an appointment with the good sister to flood this
• How one never 17 across if one makes an appointment with a Sister
• Entertaining sister, I had had a meal in swamp