flyingcheesehead
Taxi to Parking
My understanding is that the 5 sumps per wing in the later 172's and 182's is because the ribs in the integral (wet) wings could trap water which could make it to the engine after turbulence. Suddenly, it doesn't seem so useless, does it? (Not that it isn't still a hassle, but at least it isn't a pointless hassle! )
I never said it was useless... In fact, somewhere out on the interwebs there's a guy who says that 13 isn't nearly enough - He's got a new 172 with the top of the wing open, pours water into the fuel, sumps from all 13 until they're clean, and then shows you all the water still remaining in the tanks.
Of course, even with the bladders I think you're supposed to grab a wingtip and rock it up and down a bit to dislodge any that might be trapped in a wrinkle or something.