My planetary transfer vehicle was based on a core of three long Mk3 Liquid fuel tanks with four radially mounted slanted 1.25M to 2.5M adapter tanks. Fuel feed lines went from the fore and aft tanks to the center and then from the center tank to the radial slanted adapters. Tri-couplers went on the adapter tanks for mounting the LV-Ns, and then I built out the rest of the craft. My unmanned version tested in sandbox got into orbit with nearly a full load of liquid fuel at just over 30,000 units (150 tonnes) in just one launch, but when I recreated in in career, I decided to adapt the design to a mid-body puller and add a Mk3 crew cabin, cockpit, and a lots of other extras so it could be an in-orbit resource to quickly knock out contracts. Unfortunately, the fuel feed lines from the center to radial tanks weren't working correctly. I still had ~6,000 units of fuel and ~7300 of L-Ox in my ascent stage when I made orbit, so I used that on my next burn, when I fired off my injection stage, I didn't use all of the fuel in those tanks, and manged to snag a really low periphrasis for Munar insertion. As attitude changes for VERY large craft are want to do, my periphrasis lowered without me noticing and I ran out of fuel before I figured out it wasn't transferring. A period of frantic fuel transferring (gotta get all four radial tanks with some fuel else asymmetric thrust) ended when the very end of the Pegasus clipped a mountain top, causing the most spectacular explosion I've seen since that one time I turned on infinite fuel, hacked gravity, and reentered atmosphere at 48,000 m/s...