Don't you think you have the Aqua muff installed upside down? Rings are supposed to be the mounting pads...
The exhaust outlet tube is the bigger one.
It's not an Aqua Muff, it's a Jetcraft Turbomuff (probably one of their Sea-doo models) and the inlet/outlet tubes have been modded, they are normally the same diameter. Also, he had it backwards originally, but now has it the correct orientation regarding exhaust flow inside.