or you can use carve ....
so you put a little brush into a big brush and then select the little brush first and then the big brush ( holding cntrl so there both selected) then go to tools/carve , this will make a hole in your big brush the same size as your little brush
don't carve with cylinders and any other strange brushes cause it'll get complicated
Wtf is that ? its a bird ! no its a plane ! amm maybe its a plastic bag . NO ! its SUPERJER ! the greatest super hero ever!