Its really simple, It only works at donald dock (Unless there is some toon at your estate). Just go in the water. Now, Click on a toon and do report or ignore then click cancel. You should be walking under water. It works every time.
I don't use cheat engines becasue, you could get banned. I will promise that I will only do glitches and the free membership is not with a cheat engine. P.s. I woudn't use a cheat engine if I were you because Like I already said, YOU COULD GET BANNED!!!