Check your thumbnail storage settings. It could be that the generation and storage of thumbnails is causing a large file size. Can you switch your file so it uses external container storage? This should eliminate container data from your file size.
Also, I believe the recovery table can be deleted, and it does take up a substantial amount of space. Back up your file, remove it, compact it, see what the result is.
Wasn't corruption. I had a script running for the "Today" FileMaker 6 problem. This script updated 300k records every night (server side script). I had introduced an audit log into the databases and the logs were increasing by 1GB / month. See https://www.excelisys.com/fm-tips/filemaker-pro-13-tip-n-trick-easy-bake-filemaker-pro-13-audit-trail/
Amazing how tiny log additions (100 bytes maybe) added up to 1GB per month.
Well, yeah that will do it... 300,000 * 30 = 9,000,000 records you were adding every month.
Not records. The audit logs are in a text field. I was simply adding a new line to the text field.
"Wise man once say that bytes are bytes, no matter what form they take"
Cheers to figuring it out, either way!