Seems like the phrase in itself is quite self explanatory, but for those who miss the purpose; 'whatever floats your scrote' is a way of expressing nonchalance or easy-going-ness toward as subject or matter. If someone asks you to make a decision, this phrase can be used to suggest that they choose instead, and that you are happy to go with either option.
"Hey Sean, you want the raspberry or the lemon flavour?"
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. PenguinBooks,1992. p. 38)