We had a similar issue and our Trilogy is probably plumbed the same as your's. When you remove the cover over the water manifold and look behind it (use a flashlight) you can see where the black tank flush connector is hooked up to a white, braided 1/2" hose. This hose developed a kink over time and cut off the water flow, the fix is to disconnect the hose and install a 90 deg. elbow - 10 min. tops.
Take a pic. with your cellphone and take it to the hardware store and ask an employee to help you find the correct fitting if you're unfamiliar with plumbing.
2013 RAM 3500 Dually Longhorn
2014 Trilogy 3650RL, W/D, Onan 5500, 8000# Axles, IS, 960 Watt Solar, 6x6 Volt Battery Bank, Freedom SW 3012 Inv/Charger