I also kept melting my exhaust hose on a 1100stx. It was because water was not flowing in the hose and out the rear exhaust.
On top of the first front muffler there is a small elbow screwed in with a cooling hose attached to it. Unscrew it and look inside there. I had a small rock stuck in mine causing water not to flow into the exhaust itself. I stuck a small screwdriver in the hole in the muffler to get the rock out. Make sure you get whatever was stuck in there, out of the exhaust before you start it.
Also follow the lines that run back from that muffler elbow to the T elbow under the manifold. make sure they are clear by blowing in them.
If everything is clear, you should see water come out the exhuast when you flush it and run it.