Not sure if you want to purchase a house with an underground heating oil tank?

Both removal and abandonment in place are methods of decommissioning available for the purposes of the Seattle Fire Code.  However, the Seattle Fire Department strongly recommends the oil tank be removed.  If the method of decommissioning of the oil tank is to be abandoned in place, the tank must be filled with an inert solid material (e.g. sand, concrete slurry, foam, etc.).  When abandoning an oil tank in place, the interior of the tank must be tripled rinsed and washed to remove as much residual product and bottom sludge as possible.