Question about wire inside of tubing
Underground conduit will fill with water. Fact of life.  That's why you use wet rated wire in conduit.  

You can direct bury cable or wire made for direct burial such as UF.  It is made to be in contact with water.  

If you use conduit you use wet rated wires like THWN.  You can use wet-rated multiconductor cable if you really want to, but you will need bigger conduit and the pulls will be much harder.  

Using NM outdoors is out of the question.