You've probably done this, but when in doubt, when new, we've always opened one dump valve, then run one thing at a time to see if anything comes out. Open next dump valve and run each item, etc etc, taking notes of what goes to what tank. If nothing ever comes out of the dump for that tank, might attempt contacting Jayco with your VIN and sometimes they can help out with schematics. Hate you're having all the issues. We've been there several times in the past. Last fifth wheel we had had 5 tanks. Factory and paperwork said 4, none of the capacities added up to what they were saying or advertising.
John and Rebecca Dickson
Emma-8 / Little John-5 / Iva-1+
2013 Ford F-350 Lariat FX4, CC LB PSD, DRW
2015 Jayco Jay Flight 28BHBE (#8)