Draining the Hot Water Heaters

When we first moved in, we drained the hot water heaters on a regular basis -- like every 6 months, and had lots of stuff coming out to show for it. 

Now we haven't drained the hot water heaters since they were put in, about 10 years ago (March 2004).  But it nags at me to be done, so this morning I drained both the hot water heaters.

And what did I get?  Not much.  I drained the hot water heater in the hallway into the guest bathroom tub, and this is all I got: