We at The Melbourne Guttering Company always recommend upgrading your existing downpipes to 100x75mm from the old standard, 100x50mm (where possible). The extra 25% flow capacity and 50% volume with the 100x75mm helps to ensure that minimal debris is able to get stuck in your downpipes and cause water to backup into the gutter and house eaves.

Alternatively, more complex downpipes can be created through use of Harris Plumbing supplied, PVC.