One other option, as Discodermolide noted in a different thread, is simple heat activation without a vacuum. Burfield, Gan, and Smithers discussed this in an article in J. Applied Chem. Biotechnol. (1978) 28, 23-30. They dried their sieves at 300-320 °C overnight, although they say that activation is complete in three hours at this temperature. Elsewhere they recommend 250-300 °C for active sieves.