The mixing elbow is the silver and rusty object just behind the engine. As you can see it is not very easy to see how it bolts on to the engine.On the Hunter 31 I found that it was easier to go into the aft berth and remove the cover over the batteries and transmission to gain additional access. There are four bolts that hold the exhaust manifold to the engine block. These are fairly easy to get to and swing a wrench. I used a socket wrench with an extension.

See another view of the exhaust manifold.

This is another view of the exhaust manifold and the mixing elbow.

See This is a view after removal.

This is a view of the elbow and the exhaust manifold after it has been removed from the block. If you will notice, there is a nipple that stick up on the back side of the elbow (silver/rusty part). This is connected to the raw water intake. Be sure to turn OFF the raw water intake before you start this procedure.Removing the black exhaust hose can also be difficult. After 10 plus years of exhaust heat on this hose it was welded to the elbow. I had to get a screw driver and shove the blade in between the hose and the elbow to loosen it up. Then I sprayed some WD-40 in there and let it set. Then I was able to take the hose off the elbow.The next step involves removing the elbow from the exhaust manifold. We did this in the shop at the marina. If they did not have a torch, we probably could not have seperated the two parts. The fitting that is between the manifold and the elbow has reverse thread on one side or the other (do not remember which side). The entire assembly was rusty. After heating the parts with the torch, we finally were able to put a large pipe wrench and breaker bar on the elbow and seperate the elbow and the manifold. We removed the fitting and were ready to reverse the process. We put anti-sieze compound on the manifold threads, the threads in the elbow and on both ends of the fitting and reassembled. Then we were ready to reinstall the assembly on the engine. 

See Exhaust manifold gasket.

Here is the assembly ready to be put back on the engine. If you can get a can of spray adhesive it makes this a lot easier. I only had some rigging tape, so I place a couple of pieces of tape on the gasket to hold it in place. This process took a couple of tries. Once you get the first bolt started you are almost home. Be sure to use anti-sieze on the manifold bolt threads too. Torque the bolts down. Reinstall the raw water hose and the exhaust hose. Turn on the raw water intake and check for leaks. If there are no leaks you are ready to start your engine. Check for leaks again and let your engine warm up. Check for loose hose clamps or any other obvious problems. Be sure that your anti-syphon loop is straight up/down and you are pretty much ready to go sailing.