Can you not actually see the tank to check the level? When we first got our Georgetown, there was no documentation showing where th FW tank was located. I finally tracked it down by listening to it fill.
It turned out that there are two cupboards down at floor level where the queen-size bed snugs up when the slide is retracted. For some daft reason, both were fastened closed by screws through the doors into the frame. I'd assumed they were dummy doors to look like the upper wardrobes. I took the screws out and opened the doors and there was the FW tank. There's actually a drain line going out to somewhere near the back bumper with a hand valve. Opening the valve drains the tank.
Your brand may not have a similar configuration, but it's worth a look.
Frank and Eileen
No longer RVers or FR owners