Method 1:
Right Click on Health (Submission) --> click on Show find panel
Type in: Unhealthy, select all sites and delete them
Now type in "Suspended" and delete them too. This will find all sites that are unhealthy or suspended for account creation or bookmark submission.
Method 2 (this is what i do):
1. Create a txt file with all your scraped bookmarking sites (my file has 50k sites)
2. delete all sites (you can backup your data.bmd5 before doing this, this way you can use your backup database later if you need, just drag it in the bmd5.exe or double click the database and it will open)
3. add all sites, that you have in your txt file, i do this once or twice a month
I scrape fresh sites regularly and can filter duplicates with scrapebox, so i only add new sites to this file. I also filter the list from bad words (sexual words, poker, gambling, spam, scam, advocat, co.cc etc.) before adding it into this file. You can do this with scrapebox too.
Hope this helps.