The two together should be the “low point” drains. Normally one is blue and one is red. They will be the lowest point in the fresh water delivery system. If you open the, and then go inside and open all the faucets it will allow gravity to drain the water out. Easy to figure out which is which if the water heater has hot water in it.
The drain off by itself will be for the fresh tank. Draining it after each trip is a mater of personal preference, and I would check with the campground before I dumped it on site. You could run the water pump and put it in the black/gray tank and then dump at the waste station.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.