As for the "white substance" it is most likely calcium from the water, and if it has became hard, the only way to properly clean it out is with a pipe tap, that will re-thread the threads and also clean out the pipe dope and the calcium build up in the back threads.
I have had a tap for this purpose for many years and every spring just run the tap up the treads and i am good to go with a new anode rod.
Hope this helps and Happy camping
2010 Cedar Creek Silverback 35ts
2001 GMC 2500HD w/ Allison & 8.1