Hello; I haved a friend who has/had a big spacewalker on floats with a 300 Saito in it. It was so loud that he would taxi to the far side of the lake before he would takeoff, then fly it far away. It sopoiled his enjoyment of teh plane, he eventually sold it off at a huge loss. I would run the two pipes into a can of some kind and seal the gaps with JB weld, then run a copper or brass pipe out of the can. I have flattened the pipe and drilled holes in the part that sits inside the can. This has worked for me in the past I prefer quiet planes, I don't like to work in a noisy environment so I don't want to punish myself while flying. I hope you find a solution for your problem