So constructed or contrived as to prevent leaks or leakage.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "leakproof" in a sentence
"For faster results, place it in a leakproof bag and immerse it in water, changing the water every 30 minutes or so."
"And most leakproof of all is the man who is actually making the decision."
"One reason for the feverish running-mate speculation is that those who actually know anything are a small, leakproof circle."