If you don't want to drain ANY boiler water, somewhere on this site is a description of a drywell made out of copper pipe and fittings that drops in from the top. You just need to drill a hole in the top of the water chamber and drop it in place. the temp sensor then drops down inside the copper pipe. There should be plenty of wire on the sensor, I had to coil a bunch of mine up when I installed it.
My Shaver manual talks about using boiler water treatment by Wood Boiler Solutions LLC (WBS). I keep reading about the expensive stuff Shaver pushed, but I never did get that pushed on me when I bought my Shaver. WBS has not only the treatment solution, but they have chemicals that you can also flush, clean and passivate your system. They have always been very helpful to me. When I cleaned my stove, I did not want to circulate all of that stuff thru my lines and heat exchangers, so I just ran a short pipe between my inlet and outlet on the back of the stove, fired up the stove and added the chemicals and circulated it according to the instructions and only in the stove, not thru the rest of the system. Once I flushed it, then filled it with their 101 solution. I am only on my 2nd heating season, but have not had any problems yet. I just tested my Nitrate levels tonight and they are holding up. If you call or email WBS they can probably get you headed in the right direction. Weld Rite should honor their products since they are referenced in the owners manual for their stoves.