Copper wrap on stack as preheater

very slowly and if you kink it can be squeezed out some what with channel locks

Trial and error...Here's what I finally did.
The stack for the evaporator was 8". I took an 7" diameter piece of stove pipe and wrapped the copper around the smaller pipe. As it was hard to bend the tubing tight to the pipe, by the time this was done it just had to be sprung slightly to slip it over the 8" pipe.
The preheater was 2 - 25' runs of tubing. I straightened them out and laid them on the floor, used small band clamps to hold them together, and rolled the pipe along the floor and coiled the tubing around.

I wouldnt see why you cant put a valve at head tank, then a tee with one end going toward stack the other end as an open breather extending above the head tank. Then open valve accordingly, err on shorter length of tube to prevent scorching before it exits into the pan. With no bottom valve, line is never storing sap on stack and with valve being before tee any expansion/steam just vents out the top.

My plans were 3/8s as well. I plan on using a 8" stack so that bend shouldnt be to bad. If it starts to kink fill it with water and freeze it.

I purchased a 2 X 3 mason with a preheater. Is there any benefit of doing this and having the tubing empty into the preheater?