Sorry Martin, on the purge side of things....
It depends on whether you are using BW 3.,5 or BI 7.
If you are on 3.5 on the Tools menu there is an option to Delete Query Results.
If you are on BI 7:00 then the link tell you all:
SAP entertainment: Migration of 3.x objects to BI 7.0
- Delete query results.. para.