My 3x8 Thor pans have a 1" back drain, if I were to do it again, I'd get 1.5" drain on the flue pan. I have a Lapierre flue pan washer and a 1.5" drain would keep the flow at the bottom of the channels moving better.
I bought my Thor pans because of a Blaisdell recommendation. Glad I did, the price was about 40% less than Leader's quote and the quality is top notch. Welding is perfect. The best part is that I had the sides built 4" taller than normal on both pans and the cost was only 40% of what Leader wanted for normal height sides.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.