Once a year you should always empty your nestboxs. The main problems people seem to have is the issue of what you will find in them or are you just too lazy to do this, or does the wife ask you why are you taking the hoover outside? Sometimes the old nests have little visitors, such as, spiders, insects, bugs, ticks, lice, should i go on, are you feeling itchy yet?
Well the first photo shows what happens after the blue tits have moved out with their fledglings. A wasp moved in and started turning it in to a home fit for a wasp.
The best way to empty any nestbox is to place your hand in and grabbing the nest and throwing it away. Then flush with hot water, if you have a lot of boxs use some flasks.
There is always a down side to emptying boxs and that is when you open a nest and see that a near fledged bird just didnt make it, oh well that nature!! Other wise we would be knee deep in blue tits! (Had to keep that bit clean)