public void SetFeatureDrawOrder( 
   List<CIMFeatureSortInfo> drawingOrder
)

{
    //Within QueuedTask.Run()
    if (featureLayer.GetIsFeatureDrawOrderSupported())
    {
        var listOfSortInfo = new List<CIMFeatureSortInfo>
        {
            //Draw features in the layer ordered by Police_Precinct field in ascending order
            //and then by Crime_rate field in descending order
            new CIMFeatureSortInfo
            {
                FieldName = "Police_Precinct",
                SortDirection = SortOrderType.Ascending
            },
            new CIMFeatureSortInfo
            {
                FieldName = "Crime_rate",
                SortDirection = SortOrderType.Descending
            }
        };
        //Provide the list of FSOs to use and their sort ordering
        //All fields must exist on the layer.
        if (featureLayer.GetCanSetFeatureDrawOrder(listOfSortInfo))
        {
            //Set the FDO to use the list of FSOs
            featureLayer.SetFeatureDrawOrder(listOfSortInfo);
        }
    }
}

{
    //Within QueuedTask.Run()
    if (featureLayer.GetIsFeatureDrawOrderSupported())
    {
        //will throw an InvalidOperation exception if the layer does
        //not support FDO
        featureLayer.ClearFeatureDrawOrder();
        //Passing an empty or null list to 'SetFeatureDrawOrder()' will also clear the FDO
        featureLayer.SetFeatureDrawOrder(new List<CIMFeatureSortInfo>());
        //or
        featureLayer.SetFeatureDrawOrder(null);
    }
}