Started the overflow box today. Instead of using the 5g bucket idea, I used a piece of 12" round PVC I scored for a reasonable price of FREE!!!!. Once cut to size, I made a 1.5" deep weir at top using a circular saw and angle grinder to widen the cuts.
Used "hot glue" to glue my rock rubble to the PVC. Pond foam is perfect for this type of project. Not only does it help secure the rocks in place, you can carve shapes and texture by removing or adding more foam.
I added two 1" PVC couplers on opposing sides to help give me a solid mounting point for two rock arms to extend off of the overflow. Doing this will allow me to remove them for cleaning ect.
Once the foam cures I'll cut more out to reveal my gaps and shapes of the rocks. I'll brush on epoxy and spread more rock and various size sand grains for s more solid rock look.