Can not find drain on2011 blue ridge fresh water tank the belly is totally enclosed and can not see any tanks at all

Disconnect clear water supply/hose. Turn on 12v pump. Turn on the sink faucets and open the grey water drain. Wait until the faucets start spitting water (you'll know).
Complete.
If you wish to split hairs yes there will be residual water left somewhat in the system but the tank will be emptied. Good luck and happy camping

Fresh water drains should go directly onto the ground, not into another tank. I'd think a previous owner made the modification you describe. I'd correct it and allow fresh water tank drain go onto the ground.

The drain valve is open

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Typically, when your unit is winterized, the tanks and hot water are emptied; at least they should have been. What you need to do is connect a hose like you would to use fresh water and open the valve. Then go to reach faucet in your unit and open them, one at a time until the pink fluid goes clear and then wait another 10-15 seconds before closing. Once all faucets, shower and toilet have been purged of anti freeze, Make Sure the bypass on the hot water heater is opened to let water fill the tank before you turn on the power, for electric, to prevent burning up the heating element. Once all is done, you should be able to do the valve to have water directed into your fresh water tank. For future reference, the drain hose will be at a low point, under the belly with a valve. If the lever is online with the drain hose/tube, the line is open. Make sure the lever is perpendicular (90 degrees) to the line to be closed so you can fill the fresh water tank.

This is not just for your camper, but general troubleshooting.
Drain the water from the belly pan. Hook up water supply to shore water source. With water source turned on, allow some time, 1-4 hours, and check if water has returned to belly pan. If water is present then the problem is with the fresh water system. If no water, either it is a small/slow leak or the problem is not with the fresh water system. Next test the grey water tank by pouring some red food color into the shower or sink drain. Flush it into tank with water. Again, wait for some time, maybe over night, and then check for red water in the belly pan. It may take longer for the leak to appear as the grey water tank does not have pressure. If no water, check the black water tank with green food coloring and same technique. If there is colored water, red or green, in the belly pan, then the leak is with associated with the grey or black water tanks. If no water is present after these tests, then the leak may be very small and it may take days or weeks to have water re-appear. In any event, clear water is fresh water system, red water is grey water system, and green water is black water system. With any of them, checking the tanks themselves and all pipes and connectors to/from should find the leak source. The last possibility is that water is entering the belly pan from a roof or vent leak. Check to see if water returns to belly pan after a good rain. If so, the water may be clear or slightly dirty. If it is a roof leak, I have found the best repair is to use Peel and Seal roll roofing It is light weight laminated aluminum and self sticking. Cutting and applying narrow strips 4-6" wide, will seal any caulked area. It costs $95 (3' x 33') at Lowes. A 30" motor home can be completely covered with three (3) rolls, in half a day. I have re-topped 5 motor homes (one 7 years ago) and no more leaks on any of them. The product was developed to seal the roofing joints of mobile homes. Topping should last 15+ years.

U SHOULD HAVE A BLACK TANK AND A GRAY. TOWARDS THE BACK WERE U HOOK UP THE HOSE FOR DUMPING U WILL SEE TWO LEVERS ONE IS FOR BLACK ONE IS FOR GRAY. AND IF UR TALKING ABOUT FRESH HOLDING TANK LOOK UNDER NEATH AND U SHOULD SEE A PLASTIC NOSEL WITH A TURN VALVE LIKE WHAT BOX WINE HAS TO PURE A GLASS

Should be right on or near the fresh water tank.

There should be a fresh water fill on the outside of the coach. If not then there is a valve that would need to be turned that will allow water to be put into the fresh water tank. If that is the case then it will be a bit more difficult to put bleach into the fresh water tank but not impossible. There will be a pump that draws fresh water out of the tank. You can disconnect the input and output lines. Connect the input line which comes from the fresh water tank to the output side of the pump. Then using a flexible line with a 1/2" pipe thread fitting, connect that to the input side of the pump. Put the loose end of the flexible line into a gallon of bleach and turn the pump on. It will draw the bleach out of the container and pump it into the fresh water holding tank. Now return the plumbing of the pump back to the original configuration. Using the valve system complete filling the fresh water tank with fresh water and allow to sit for a couple of days. Then open the low point drain on the fresh water tank and completely drain. When the coach is not in use make sure the tank is completely drained. There is also a fresh water treatment that you can purchase at your local rv parts department.

That's only at the bottom or its sides. Just look for it at on four corners of its bottom and all sides...