It's not with rclone.conf on MacOS apparently.
Just going to post this here for reference (as I don't think it's in the docs)
I tried:
rclone mount crypt: ~/Desktop/rclone --vfs-cache-mode writes --vfs-cache-max-age 10s -vv
with the thought that if I couldn't clear the vfs cache manually (or find it) that rclone would just purge the cache on its own after 10 seconds. That did not work.
Then I ran: rclone mount crypt: ~/Desktop/rclone --vfs-cache-mode writes --vfs-cache-max-age 10s -vv
The console output with -vv was different:
2020/02/20 12:00:34 DEBUG : rclone: Version "v1.51.0" starting with parameters ["rclone" "mount" "crypt:" "/Users/lebowski/Desktop/rclone" "--vfs-cache-mode" "full" "--vfs-cache-max-age" "10s" "-vv"]**
2020/02/20 12:00:34 DEBUG : Using config file from "/Users/lebowski/.config/rclone/rclone.conf"
2020/02/20 12:00:36 DEBUG : Encrypted drive 'crypt:': Mounting on "/Users/lebowski/Desktop/rclone"
2020/02/20 12:00:36 DEBUG : vfs cache root is "/Users/lebowski/Library/Caches/rclone/vfs/crypt"
The bolded line did not appear in the console output when I ran with --vfs-cache-mode writes, only when I ran with --vfs-cache-mode full
I deleted the entire contents of ~/Library/Caches/rclone/vfs/ and restored about 9GB of space.