Can't help with the water pump issue but the black tank is probably empty. Those gauges NEVER work properly. Not just a Forest River problem. Put a clear fitting inline ahead of your sewer hose and you can see when it's empty when dumping. I never look at those gauges, most people don't. The toilet will "burp" when flushing to tell you the tank is full. The sinks and shower will start to back-up when full. I usually don't close my gray tank valves when I have hookups. No reason not to just let them drain.
Refer problem is the pilot ignitor may need to be adjusted a little closer to the flame. Very easy adjustment.
If these are the only problems you are having with a new unit you're lucky. They all have issues.
2015 Chev Silverado 3500 dually D/A
2016 Cedar Creek 36CK
B&W Patriot 18K, Trail-Aire pinbox,
Level up, dual panes & all that stuff...