How to get bubbles out of buttercream?

[SunnyAgain]

I've been making lots of cupcakes with buttercream swirls, and can get the swirls in a good shape but find the buttercream has bubbles in it so the surface get "pock marks". Is it the way I'm filling the piping bag? Or too much beating, or not enough? I can see little pockets of air in the piping bag so I suppose that must be due to not filling the bag well, so any tips on that, or general thoughts on getting smooth piped buttercream would be much appreciated!

What about using ganache instead?

I thought ganache was only made with chocolate? I have used chocolate ganache on chocolate cakes (and it was yummy!) but for vanilla cupcakes I generally make vanilla buttercream, which gives me the option of tinting it different colours.

Maybe the icing is too thick?

I thought that may be the problem but the last lot I made I put a bit more milk in so it was very soft, and when I piped it into the swirls they looked less smooth than ever. Very frustrating!