I purchased a wand and cleaned my water heater tank for the first time after owning the MH for two years. One winter was in Phoenix and the second was in Texas, both of which have horrible water. I also cleared out a tank of big chunks.
It you buy or build a wand, make sure it is long enough to reach the bottom and corners of the tank without trying to force the shut-off valve into the tank. I cleaned mine from the top, through the emergency release hole while having the drain valve open on the bottom. My logic was that the build up should be thinner at the top and, therefore, easier to break through to get the cleaning process started.
I probably spent an hour concentrating the wand on one spot and then the next as the discharge indicated the first spot was reasonably clean. However, it takes some time to initially get the build-up to start to break loose and I imagine that someone who simply rinses the tank with a hose believes the tank is clean because without a wand and good concentrated water pressure... and time, it won't break loose.
I also concentrated on the check valves in an attempt to clean them also.
As Rene said, that stuff is thick, and in my case, even after only two years of use.