Overflow protection for a rainwater tank is very important design feature. 

By using a well designed overflow system you will protect vermin and insects from entering your rainwater tank. The overflow system is installed inside the rainwater tank. In underground tanks it is a critical requirement as it also protects the tanks from any back-flow that might occur in the underground storm-water piping. 

The Wisy multisyphon overflow is made of impact-resistant ABS plastic. It has a 100mm connection . Surface debris is  removed by a skimming effect. It prevents storm drain odors from reaching the storage tank. A Brace pipe prevents tilting or tipping.