It is a place to stick my carbon bags
I originaly bought it when i had my planted tank. I was going to fill it with bio balls. I had the container, thought I'd better use it... I was going to use y 20g for a sump, but the dremel bit to drill it for a bulkhead was $16, the rubbermaid was $17.. I ended up cutting up and using the 20g to make my overflows
Walter