Possible Clues:

• One foot with a knock that's left in glass
• He leapt out to get the last drop
• If there's only a little drink left, put your foot down
• Help! Tea has been brewed but there's little left to drink
• Knock it at the bottom of the glass with the bottom of your foot
• Drop left in glass
• That's what's 33 down if you put your foot down
• Tilt and extract remains of drink
• Putting your foot down for what's still in glass
• Bit of booze left in a glass