Possible Clues:

• It's a comedown, though some evidence points the other way
• Squalid joint
• Type of starter band gig
• Use the springboard
• Compete at a pool in the Olympics
• Submerge
• I've come across hundreds on the way down
• What footballers might do illegitimately in dodgy club
• Is it hundreds I have to get to take the plunge?
• Sub captain's order in sleazy pub?