Dear Ben,
It may help to think about modeling the piece in much the way it would be fabricated for real in, say, a metalworking shop. In other words, the two bell shapes at each end would be done separate from the straight tapered piece, with two elbows joining everything. The bells and the straight tapered section can be modeled with the Follow Me tool; they’re simple extrusions. The elbow sections that join the straight part to the bells are probably the hardest parts to model. They might be easiest to do with a plug-in like Curviloft; it allows you to model an elbow shape with different diameters at either end. Actually, you’d model just half of each elbow, then copy, flip along, and connect the two halves to make the curved section. I’d also advise modeling everything at 100x its finished size. That will allow you to avoid a problem with SketchUp–not filling in very small faces in extrusion or lofting operations. When you have the 3D shape you desire, scale everything down to its actual size. Or, make the necessary profiles 1:1 and make each a component; make a copy of each component, scale up the copy, and do the extrusions and lofts. Then simply delete the copy. The original should come out just right.
Hope this helps.
Best,
dh