I'm not sure which version of bleachbit is ok, however as you said it's ok for you to use another program, I'm going to suggest another cool small utility for this purpose.
To wipe free space I recommend sfill
program from secure-delete
package.
Installation:
sudo apt install secure-delete
It's got a bunch of cool stuff:
$ dpkg -L secure-delete | grep -i /bin/
/usr/bin/sswap
/usr/bin/sdmem
/usr/bin/sfill
/usr/bin/srm
sfill
is for wiping free space, usage:
sudo sfill /
It will write the whole disk 38 times. you can use switches like -f
to make this process a little bit faster. or for each -l
it will decrease the number of writes.
For example
sudo sfill -fll /
Wipes the whole disk one times and fast.