I don't know much about DP's, I'm still on my first gasser, but I have been told my 75 gallon tank is only going to fill 80% due to the filler neck joining the tank on the side, not the top. Also due to the air bubble.
When gassing-up after running on fumes, I can tip the rig toward the passenger side with my left rear jack and force feed it up to 65 gallons, but that's about tops. a 150 gallon tank might top-out at 120+ under the same conditions. Just wanted to mention it.