Drinfeld double is a construction which out of a discrete quantum group Gamma produces a locally compact quantum group D(Gamma) by gluing together Gamma and its compact dual. Both quantum groups are located inside D(Gamma) as quantum subgroups. I will describe how in such a situation one can average functions on D(Gamma) into bi-invariant functions. In the second part of the talk I will introduce amenability and its weak variant, and discuss how one can use averaging to obtain relation between approximation properties of Gamma and D(Gamma). The talk is based on a joint work with Matt Daws and Christian Voigt.