The Old Man and the C Student - S10-E20
Corrected entry: Homer flushes his springs one by one and sings a parody of "10 green bottles", but with flushing springs. He goes from 999 to 996 but doesn't flush the toilet enough times to get to that number.
Correction: While Homer is flushing the springs, it goes to Marge at the door. Homer must then put in more than one spring, then start singing again.