You can use LDP.EXE to do the garbage collection control. Here are the steps:
In Ldp.exe, when you click Browse on the Modify menu, leave the Distinguished name box empty.
In the Edit Entry Attribute box, type “DoGarbageCollection” (without the quotation marks),
In the Values box, type “1” (without the quotation marks).
Set the Operation value set to Add and click the Enter button, and then click Run.
It is possible that the garbage collection you start using the above method could stop in favor of more important tasks like AD replication in the same way as the scheduled garbage collection does.
If that happens you can simply repeat the garbage collection steps above until all of the objects are removed.