Don't let it dry out or it will take over a year to re sink. Here is what I have done in the past. If you can get it to fit into a large cooler that is best because the insulation will keep the water warm for 3-4 days otherwise use some kind of a large bin.
1. Use running water and a strong bristled brush, and scrub all of the loose material off of the wood. Then rinse
2. Place the log in cooler/bin and fill with hot water. If you have a python. hook it up to the sink and use the hottest water possible.
3. Add bleach. I normally use 3+ cups. Just to kill everything.
4. Soak for 3-4 days
5. Scrub and rinse again.
6. If you are worried you can soak with bleach again, but in my opinion everthing should be dead. So I normally just soak again in plain hot water for a 3 day. If you want you can add prime.
7. Then just pull out, rinse, and in place your tank. Only a one week process.