It seems like the right thing to do to keep your raingauge funnel clean and shiny so that rain runs easily down to the base and through to the buckets but I have recently found out that this is actually counterproductive. It's fine (indeed essential) to check regularly for debris in the funnel (yes, we're back to the bird issue again) but actually cleaning the funnel surface of the general dirty film that grows on it should be avoided. The plastic raingauge, indeed all raingauges, slowly build up a thin film of metal oxide or a fine cover of ingrained dust which covers the underlying material and this can help stop the formation of large drops and so aids draining – so don’t clean the raingauges! If the collector has a clean shiny glossy surface it may actually stop the flow of water until the drops get very big.
My thanks for this information to Ian Strangeways, who is a well known expert on raingauges in the UK and has done a lot of work on them all round the world. No more polishing for me then........
