Flushmem was removed from Blitzmax. It's garbage collection is automatic unless , you go manual.
Function GCSetMode( mode ) Description Set garbage collector mode. Information mode can be one of the following: 1 : automatic GC - memory will be automatically garbage collected 2 : manual GC - no memory will be collected until a call to GCCollect is made The default GC mode is automatic GC. Function GCCollect() Returns The amount of memory, in bytes, collected. Description Run garbage collector. Function GCMemAlloced() Returns The amount of memory, in bytes, currently allocated by the application. Description Memory allocated by application. Information This function only returns 'managed memory'. This includes all objects, strings and arrays in use by the application.