You’ll typically need to let the silicon dry for at least 24 hours. After that, check to make sure you don’t have any leaks. If you find a small one, just dry the area off and try some more silicon. For aesthetics, you may consider painting the barrel. We would suggest rustoleum for plastic (or whatever your barrel is made of). Put it in place, connect your downspout and start saving the world (and money)!
Don’t be intimidated by this project, the only quality you need for this is openness to trying something new. The materials and tools are quite common. If you’re missing something to get the job done, surely there’s someone in your family or community that can lend it to you. If you have any comments or questions, please visit theahimsaproject.com