i have a usb thumb drive that i mounted and did stuff with, then when i went to umount it it said it was busy (showed twice) i did lsof and fuser on every file on the drive including the mount point itself and all devices (sdb and sdb1) in /dev related to the device, everything said nothing was using it, so i decided to go into single user mode, and it was still busy, i eventually did a umount -l and that said it umounted it, but i don't think did it the correct way (the man page says that just removes it from the file system without actually umounting it all the way), then i pulled the drive out and haven't seen any problems but was wondering what to do if this happens again, is it right to just umount -l and then putt the drive out, or should i try something else?

You weren't cd'd into the directory it was mounted to were you? Say you mount it to /mnt/usbdrive and nothing was accessing any files on it. But say you cd'd into /mnt/usbdrive so it was your present working directory, you will then get a "drive busy" error when trying to umount it.

yea, i realize that could happen so to verify that i was using fuser right i cd'd to the directory and ran it again, that time i saw 1 PID of bash, i then closed that terminal and fuser once again started reporting that nothing was using anything there

try

$umount -l mountpoint

If you have an LED on the thumbdrive that indicates it's in use, obviously wait until the LED has gone off. Then you could try forcing write of anything in buffer that hasn't made it to the device yet with the "sync" command.