A few months ago it was pointed out that a lot of garbage was being imported into the P6 database via xer files similar to the way that POBS tables were causing the database to grow very large in size unnecessarily. If you look under Admin then Admin Categories and look under the Risk Types tab you may see a lot of junk risk types there. To clean these you will have to manually delete them. However in the future you can clean the xer file of the POBS tables AND rubbish Risk Types prior to importing the xer file into the database. A big thanks to Ron Winter for looking into this and modifying his POBS cleaner program to include the Risk Type cleaner.
Here is the link to his revised cleaner