To empty recycle bin data in Salesforce using external application, emptyRecycleBin () method is used.
Delete records from the recycle bin immediately. The recycle bin lets you view and restore recently deleted records for 15 days before they are permanently deleted. Your Organization can have up to 5,000 records per license in the Recycle Bin at any one time. For example, if your organization has five user licenses, 25,000 records can be stored in the Recycle Bin. If your organization reaches its Recycle Bin limit, Salesforce automatically removes the oldest records, as long as they have been in the recycle bin for at least two hours. If you know you will be adding a great number of records to the Recycle Bin and you know you won't need to undelete () them, you may wish to remove them before the Salesforce process deletes records. For example, you can use this call if you are loading a large number of records for testing, or if you are doing a large number of create ()calls followed by delete() calls.
EmptyRecycleBinResult = connection.emptyRecycleBin(ID ids);
where connection is an object of EnterpriseConnection.
Sample JAVA Program to empty recycle bin data in Salesforce