From What i've encountered dabbling in any Boolians, your mistake was deleting the Polygons from the tube. you need to "Edit"the existent ones, you can convert it to editable Polygons, and after "smoothing" choose to make it a mesh welded, also "before"you boolian it try and ,make sure you "cap holes" your using 4 views or 3, but you may miss something if looking at it at certain angles..this is going strictly by old memory i recall a similar problem once. i could be wrong.