TS- No thank you-above my paygrade or skills. When I did drive, it was 7600 gallons on five axles. Of course that goes back in days when we had spokes, and tanks had two meters, two direct lines, two 4" hoses and in a 3" Blackmer pump on some tractors. My region was not in the "weight savings at any cost" mindset. In fact I remember one of the old fleet maintenance supervisors who had a saying..."aluminum is only good for teakettles". Later in my career I was the regional staff guy responsible for fleet and we were still not that weight conscious. Rest of the country was into Alcoas and we were still on spokes!
Big change came here I think when an R-700 pulling a Fruehauf bath tub dump, probably grossing over 100,000 lost control on a road under spans leading to Tobin Bridge. Knocked bridge pier out and this major span over Boston harbor was shut down. As a result of that Mass started big crack down on overweight trucks but also passed legislation raising 5 axle limit to 99,000 lbs while eliminating requirement to comply with Fed bridge formula.
Picture is what we then used- 11,800 gallons, no bridge formula, trailer tandems were 50,000 pds and the LT 9000's had 40 rears and 12 fronts. But the first time you drove one of these you knew center of gravity was VERY different. Later on rest of New England followed suit but required triaxle tanks. All that is except Conn. They are still at 80,000-and bridge formula.
Maybe my imagination but I think this may have led the push to bigger trailers-and with more axles vs. combinations as used in Michigan.