We are in the process of closing our pool for the first time. Everything was moving along very nicely, until we tried to blow the water out of the bottom drain. No water bubbles came up when using our 4.25hp shop vac. Could it be too old? too weak? Is it necessary to drain that line, since it is pretty far under ground? We are in the Raleigh/Durham area, so it doesn't usually get too cold. Last winter, though, we didn't close the pool, the temperature really dropped, the electricity went off for three days, the pipes froze, but amazingly they didn't burst. We thought we better try closing this year. Any ideas about the bottom drain?