I have that engine M35B,  view this image. You are looking at the drain plug of antifreeze that is on the port side of the engine.
You do not need to drain the antifreeze to replace the exhaust riser.
https://www.catalina36.org/sites/default/files/Sail%20La%20Vie%20M-35B%2...
I have never replaced it and know nothing about it.
I will follow this thread to learn.
By the way, edit your post, change the 26 feet to 36 feet catalina.
Visit my website on my signature to see how I replaced the antifreeze.
Haro.

Hi Kevin,

Looking to the same build period, I wouldn't be surprised if you are facing similar issues we had.
Removal of the riser is not a complicated job itself.

Also I looked at replacing the riser, but after taking out the damaged one and noticing what the issues caused, I decided to repair the original riser which is the cheapest and easiest solution.

In the attached file you see some pictures before and after the repairs.

Hope this information helps.
 

You will need to drain the exhaust manifold. The section where you add coolant. The exhaust flange on the back along with the gasket may need removal so that you can attach a new riser. I believe you will find that the threaded pipe going into that flange will be a bit stubborn. Just my guess. On my Catalina 30 I replaced the riser and built my own from threaded pipe sections, but on my 36 I used the riser from CD. 

I have a 2000 Mkii 36 with a m35b engine also. I'm seeing a tiny bit of leaking and some rust where the riser connects with the hump hose. I'm thinking of just buying from CD because it's mostly likely to fit rather than try to work on something troubling. I'll likely also buy a new flange and hump hose even though the whole package seems, it will exceed $700. Any suggestions or advice on how to replace the riser will be welcome. It will be my first try also.
 

I replaced the failed riser on our C30 / M25 engine. I used black pipe. I can't recall the specific grade, but generic black pipe will not hold up well. It took many trips to the store to get all the angles and lengths correct. With the boat some distance away, this became a problem.  Factor all the store trips and labor into the project, and the price of an insulated riser purchased from CD would have likely been attractive vs. the approach I took.  

Ive read the other posts I could find regarding replacing the exhaust riser. (Im assuming that's the same thing we all call the "water muffler" around my dock.&nbsp; And I can't find an answer to this question:&nbsp; I had a significant amount of salt water seeping onto the galley floor&nbsp; but only when the engine is running of my 94 C36 from the area adjacent to the fiberglass water muffler box so i'm sure that its the box is leaking.&nbsp; I removed the box and all the piping for both in and out ports, cleaned it and refilled it with fresh water to look for where the leaks were. but with just gravity&nbsp; &nbsp;pressure there were not obvious leaks. even though there were several hair line cracks , no water was comig out.&nbsp; I think what I will have to do next is rig up some sort of Pressureizing&nbsp;arrangement to force the leaks to show themselves. Im asling for any helpful suggestions please.<br /> Thanks, Capt. Sam

I had to replace mine on our '98 a few years back due to a leak inside one of the bolt/screw holes in a corner. I was able to get  an identical replacement from Catalina in Largo, Florida. It sent me several drawings of different configurations and I found the one that matched, ordered it and got it in several weeks. Perfect fit and no leaks.