Honestly, I could not get the achievement by bouncing off the falling soap block on Home level 11, as the other solutions mention (you can check out the video below). I even ate up all 6 duckies underwater twice. (maybe glitchy? Using Nokia Lumia 925). I gave it maybe 60 tries before I tried it a different way:
I got it on the same level (1-11), but instead I aimed for the bottom duck of the SECOND row, and I waited until the falling soap block popped all the ducks from the first row. Then, as the first row ducks were on their way, floating to the top, I released my shark, gobbling those ducks and then the second row of ducks, too. Took less than five attempts for me doing it this way. It is all about timing for grabbing those three rising ducks; the other three in the second column are easy to grab if you keep your aim steady.