Possible Clues:

• The graduate comes up for a wash at the week-end
• Graduates come up to wash at the week-end
• Religious day
• Religious day of rest for Jews and Christians
• For arrest, perhaps, and a wash at last
• The graduate's back for a wash there for the rest of the day
• 16 down is when the graduate's back for a wash
• In Sweden, pop group gets time (an hour) on Sunday
• Day for observance
• When a graduate's back, not at work at a bathtub