Yes you can but it is not good practice.
You have to filter out all the debris and leaves in your gutter and prevent it from entering the rainwater tank. High loads of organic material affects the quality (smell and taste) of the water in the tank.
We recommend that you install a primary rainwater filter.
Vortex and inline filters are very good as they are selfleaning and prevent any debris greater than 0.28 - 0.44 from entering the rainwater tank