I find the way around splashback is too let a bit of pressure build up first. That way when you crap the **** flies out with a bit of velocity at maintains the right angle to enter the water and create minimum splash, kind of like the difference between an Olympic diver and the fat kid doing a belly flop.
As for floating, mine always sink to the bottom quicker than the titanic. I find food like fruit and veges causes excessive floatiness. So stick to things like meat, fast foods, beer etc, this will cause your turds to stay down and not float (the beer also helps build up pressure too). This mixture of food also provides a nice odour, kind of marking your terrority. Everybody knows, he who stinkest the mostest, ownest the toilet.
