Mildew inside lava rock?

[musicman]

About two nights ago went over to my tank in progress and realized that it was putting off an offensive odor. I did some brief investigating and discovered that my lava rock was stinky. I smelled it in several different places and got an equal number of different smells. In general I found the faint smell of musk and mildew.

Six days ago, when I first got the rock I hadn't noticed any smell. The rock even looked rather clean. I rinsed it anyways, for good measure. Afterwords, I soaked the rock in a 5 gallon bucket. When I put the lava rock into the water in bubbled and fizzed letting off air trapped in the rock. I realized that the holes in the outside of the rock went through its entire internal structure. It was like a heavy, stiff sponge.

A sponge indeed. When I removed the rock from the bucket about two days later it bled water. I put it on a towel where it continued to let off more water until the chair underneath the towel was wet. I shook the rock out and it appeared to be empty so I found a suitable placement in the tank.

It let off more water while inside the tank! I soaked it up with a paper towel and didn't think much more of it after that. That is until now. I figure that there is still water inside of the lava rock. That moisture inside of a dark warm rock would make a fantastic environment to grow mildew. Well crap. I wanted to put that rock in my tank.

I took the rock outside and left in on the table on our back patio. It's supposed to be over 100 F for several days in a row. If anything, it should help dry out the rock. But I am afraid of what problems I could introduce to the tank when I allow the rock to get wet again.

What can I do to make this lava rock safe?