Although I've not seen the 25.2 in person, I suspect yours is under the bed. My 25.4 has a short run from the outside gravity fill to the tank and it's a straight line. The fresh drain, quarter turn residential toilet style stop, comes of the bottom and like NewAxisOwner said, it was nearly blocked. To speed up the draining I used the outside shower also. I've since repiped the drain to the outside wall. It's not a torrent but a lot faster. After you've emptied the take, locate the strainer, inline before the pump. It will be full of white plastic shavings from the installation. Lazy bums.
I'm wearing trifocals now but my hindsight is 20/20.
Bilsteins and Sumos front and rear...HUGE! FatMat and Hoodliner...HUGE!
Hellwig sway bars F&R, 235/85 Hankook ATM, alignment...HUGE!!!
Battery watering, 260watts Solar and BigFeets to make life easier.