Here is a little helper for filling the fresh water tanks that I use to help avoid the "trickle fill or gushing back out"
.....these problems are usually cause by the sharp bends or kinks in the fill and vent hoses, and yes sometimes blockages.
I use a clear 1/2" hose about 2 feet long with no end to feed down the fill opening attached to the fill hose. A shut off attachment at the coupler to help regulate the pressure and then to shut it off when it's full.
If I just stick the garden hose in the top of the opening it will back up and gush out.....so sticking the fill hose further down the fill pipe works well for me . When it is full it will dribble out the vent hole/screen beside the fill access. I have only 1 vent (at the top and 1 drain at the bottom).
Side note: I prefer to travel light so dragging along full tanks of anything only means less mpg's, unless you have no alterative and you have to haul full.
Hope this helps
'07 WildCat 30 RLBS ~ West Coast Edition ~
Trail Air - Tri Glide Pin Box
2000 F350 DRW 7.3 Diesel Lariat 89k miles
Edge programmer, 4" SS exhaust turbo/back
Vancouver Island, B.C., Canada