The average residence time tau of a polymer of length N passing through a narrow hole under a chemical potential gradient is calculated. In the proposed model, details of the hole parametrize the rate constant k(0) for transporting a monomer across the hole, independent of the chain length. We show that any asymmetry in the average conformations of the polymer across the hole is sufficient to generate the driving force for the polymer translocation. If chemical potential gradient is absent, tau similar to N-2, with the proportionality constant depending on the size exponent of the polymer before and after the translocation. For translocation along the chemical potential gradient Delta mu, tau is proportional to N(T/k(0)Delta mu) and N-2/k(0), respectively, for large and small N Delta mu/T. For translocation against the chemical potential gradient, tau similar to exp(N) for long polymers.