Tic:
I replaced my hose due to an upper re-occurring leak. I estimated 2-gallons were in the expansion tank, so I purchased 2-gallons at the CAT store before proceeding. After trying drain and capture the antifreeze with limited success, I discovered that not only do you lose tank fluid on the upper flange, once the hose is off the engine flange fluid will back flush fluid until it reaches a level point (probably around a gallon). So, I reattached the hose and re-grouped. Therefore, I can confirm that as Jim advised, 3-gallons will be lost.
I had another idea that solved the problem. Using an oil extractor pump (I use it to when changing oil on our Wave Runner). I ran the hose through the upper tank opening, down through the tank and into the engine hose all the way down to the flange. I then pumped the fluid into clean containers. I was able to extract approximately 2-gallons. When I pulled the hose, minimal fluid came out of the engine flange.
I pulled the old hose off and placed shop towels into the engine flange while going to the auto parts store. I was able to find a 1 1/4" ID hose (cut to 24" long) at O'Reilly's auto parts. Since I had the old hose, I cut the new one to the same length (around 18") and installed it on the engine and tank connection.
I bought 24" of vinyl hose from Lowe's and attached it to a large funnel, this allowed me to fill the tank from above the engine compartment door while on a stepladder. I used an automotive paint filter to filter the old fluid, re-used the 2-gallons and added 1-gallon of new fluid.
Following is a link for the extractor pump that I used.
http://www.northerntool.com/shop/tools/product_200596412_200596412Randy