HELP with landscape drain installation

I installed roughly 90' of corrugated drainage pipes in my yard yesterday. See pic. The drain will carry water from gutter downspouts to my street. I also added a few catch basins to collect excess water. Before filling the drain line with dirt, I did a test run by adding water from water hose to make sure there were no leaks, etc. When I did this, I notice a few leaky areas in places where I connected the pipes (since I bought them in sections of 10'). Can anyone tell me why the leaks? each section of pipes were connected correctly. Is this an indication that there is not enough slope in my lines? Please help...this is really bothering me! thanks!!!Attachment 39061 (http://www.doityourself.com/forum/attachments/lawns-landscaping-outdoor-decor/39061-help-landscape-drain-installation-img_4612.jpg)