Post 3 is exactly the best way. Steve's is good when there's no livestock.
A piece of 3/4 & 1" pvc long enough to get everywhere you need to and a funnel that will fit in the pipe. The narrower pipe won't flow well but gets into tighter spots better. Using dry sand is the easiest to pour but without rinsing will cloud up pretty bad.
To rinse the sand put a garden hose in the bottom of a 5 gallon bucket then add a bag or two of sand. Turn the water on and let the bucket overflow stirring as best you can. Let the water run over till its clear. Tip the bucket over and dump as much water out as you can and refill with rodi water till there's an inch or two of water over the sand. Then dump it, and then lather rinse and repeat. Do this one more time with some Prime in the rodi water.
Once rinsed good, add some sand to the funnel and slowly pour a little tank water into the funnel to get the sand to run down the pipe. Work slowly and continue till done.