I have a 2016 Vegas 24.1, I opened low point drain for fresh water tank and getting just a slow trickle that slowed to a drip. Left overnight and still did not drain. I drained it last year and this summer with no problems. The valve is parallel to the pipe which I believe is open and I cracked a faucet thinking an air lock of some sort. Maybe the airlock is in my brain and am missing something simple.
I am not familiar with the Vegas plumbing so if the drain line and its associated valve come directly from the fresh tank I would suspect plastic bits (from when Thor drilled pipe holes in the fresh tank) are partially plugging the line or the valve. The other issue may be the vent line to the fresh tank has water in it or is plugged somehow. You could just open the fresh water fill cap to allow air in or just blow any water out of the vent line to clear it. Opening taps to allow air in will help drain lines on the high pressure side of the water pump but not on the low pressure (water tank) side of the pump. When you use your water pump to draw from the fresh water tank (with valves set appropriately) are there any issues with low water flow or water pressure from the open tap? If not, then the fresh tank outflow through the water filter and pump would seem clear of obstructions. Usually plastic bits fill the filter screen during the camping season and may do so for several years until they clear.
So the issue could be a possible blockage in the separate drain line. If it is plastic bits and the drain line is a separate line from the fresh tank, you could try blowing some air back up the drain line to force the plastic bits back into the fresh tank to see if that fixes things temporarily, but water outflow may just bring them back into the drain line again (or the pump feed port into the filter). You may have to temporarily bypass the drain valve (remove and reinstall) and see if the bits can free flow out of the tank and drain line (if that is the problem).
Can you tell my wife I can take the rest of the day off?
Congrats on moving the bits.....they will be back eventually so if your pump flow is low then you likely have a water filter screen full of bits too. Easy to clean there. Make sure after cleaning bits there are no cracks in the filter lid or body and no seal air leaks......or the pump will suck air instead of water next time you go to use it.