It almost seems to me like you're going to have to wash them out with something. Those nests are really stuck in most cases. If you just poke up in there with something and vacuum, you're going to leave a lot of dirt still stuck in there. If you use water, then you have to be vigilant on getting the all water out and preventing rust. I wonder if kerosene would dissolve the nests? It would take a lot of kerosene to wash it repeatedly, which it will probably require.
Hmmmm....Good question.
Maybe someone else has a good idea.
bkay