How can I unblock rainwater drain?

Andy

Peccavi is as usual on the money. Maybe try with boiling water first if you can get some of the water out so the hot water gets to the fats. As a tip in future as you seem to be using this as a sink waste too throw a kettle of boiling water down it every so often to remove any fatty depisits, don't treat your sink as a waste disposal and try to lower the fat content of your wet waste.

kennyf
March 2009

Scrape out by hand as much congealed gunk as you can and pour in some caustic soda solution - take care - if you use too much caustic soda it will form a hard plug almost like concrete and make your problem much worse. Also take care to keep it away from your skin, eyes and any paintwork - it's used to strip paint from doors etc.

I've used caustic soda on a fatty blocked kitchen sink - ten minutes wait and a sudden glug glug glug.

Good luck...

Peccavi
March 2009