Cleaning out water jackets, with block outside car.

If you DO NOT have experience using acids and alkalis, DO NOT endanger yourself, loved ones or pets. Use any of the non toxic solutions as suggested above. Acids and alkalis can harm or kill quickly! We used to store chlorine tablets for our pool in a shed attached to the back of the garage. A neighbor asked if he could borrow a few until he could get to the supply store because he was out. He did not reseal the bucket and being humid in Texas, moisture got into the bucket. I went out a few days later to get some tablets for our pool. When I took the lid off the bucket, the chlorine gas hit me in the face. I passed out, but luckily my wife saw what happened and called 911. After being checked out at the emergency room, I was told I was lucky that it didn't fry my respiratory system. It was a mistake on the neighbors part for not resealing the container and a mistake on my part as well, for not checking. We all do dumb things and some of use survive and learn our lesson. Some of us don't, be careful!