Your water butt wont overflow thanks to this Harcostar Universal Rain Trap Diverter in (Green) which will divert excess water back down the downpipe. This Green Harcostar Universal Rain Trap connects to a round downpipe in the following sizes: 63mm, 68mm, 80mm and 100mm and also connects to a square downpipe in the following sizes: 61mm and 65mm Simply cut a section from your downpipe and insert the rain diverter. This Universal Rain Trap Diverter comes with a 0.5m quality flexible connecting hose, so your water butt doesn\'t have to be directly in front of a down pipe. Please note: This product NOT suitable for cast iron downpipes and some water butts may require a hole to be drilled in order to attach it - This is easy to do. Hose Internal Diameter: 19mm. Hose external diameter: 24mm.