D-tub Overflow Handling

Water overflow handling will be needed.   Under the rear seat will create a ~80 gallon overflow storage tank, with large perforated stainless steel sheets leading to this overflow storage tank. I will try to make the overflow quiet, too, using a trap-like pathway.

I still need to figure out where the water line will be: 3" from top of tub, 6", 9"?  I really don't know.  A 12 degree slope on a 63" diameter tub is a 6.7"

I have no idea.  I'll build the overflow system after I get some experience with the tub being towed around.