I don't have such a large portable FW tank - just a 5gal - but I did read a suggestion here about rigging an RV pump to pump it into the RV FW tank inlet. While I'm pretty economical with the shower, my DW is not and our favorite provincial campgrounds only have (at best) an unthreaded communal hydrant that is not always in range of my 100' of FW hose and Water Thief.
I've tried (and mostly always failed) to pour a 5gal into a funnel in the FW inlet but never thought of the pump idea before (naturally dumb, I suppose). I just so happen to have a good used RV water pump because I replaced the 'sick water buffalo' sounding pump in my old TT with a VSD model (the pump in the new 5er is so quiet I don't have to do that again).
I don't mind hauling the 5gal several times but it will now be more satisfying when more of it ends up in the camper than on the ground.
P.S. I have a 35gal tote-along that I put in the TV and pump into with a Flo-jet (some of the dump stations are a long ways away) so I don't overflow the holding tanks.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam