Dispose in a separate bottle.
If you do not fear the satanic sibilance and if you act very carefully and slowly you may pour the oleum onto ice. It is a good idea to perform this reaction in a big round bottom flask which is filled with ice. Use a dropping funnel with pressure equalizing tube to add the oleum. This will prevent from smoke and splatters. If an open bottle should be used an erlenmeyer flask is best. A deactivation is only meaningful if the quantity is so small that the resulting mixture may be flushed down the drain.