brew install ckesc/leakcanary/<formula>
Or brew tap ckesc/leakcanary https://github.com/ckesc/homebrew_leakcanary and then brew install <formula>.
Or install via URL (which will not receive updates):
brew install https://raw.githubusercontent.com/ckesc/homebrew-leakcanary/master/Formula/<formula>.rb
brew help, man brew or check Homebrew's documentation.