Had the day off today so I thought it would be good idea to have a look at the roof drains I flushed them out with water with a long piece of pipe and a funnel then sucked them with a vacuum cleaner a bit of muck came out but no where near as bad as I thought. While I was there I opened up the drain plug hole slightly to allow better flow? Easy job really although I did get an eyeful of gunge drop out into my eyewhen I was poking around!