Swap

I don't want to mislead you, but I believe that when you install Trisquel it creates a partition used for swap. I don't think you can wipe it.
You can however use the "memory" option and the "free space" option, which would in theory wipe all traces left behind of anything you might have been doing. HOWEVER!!! Keep in mind that "memory" option is unstable and might harm your system. Also, free space does takes a lot of time (depending on how much free space you have on your HD).
I am not saying it will clean the swap partition, but it is a good start.
I use Bleachbit, with everything on except those two, due to the reasons I stated above.
Hope it helps in some way.

Check in /dev/mapper for cryptswap1. I don't know if the installer creates this every time whether one chooses to make the home folder private or not, but if it is on your system your swap partition is encrypted.

As to wiping free space on your hard drive, that really isn't useful if your filesystem has journaling.

Are you sure that you even need to use a SWAP? Most ordinary people don't. It is a thing from the past when RAM an expensive and scarce ressource. Today RAM it is abundant and cheap for most PC's. So I think you should give it a try and install a system without a SWAP.

Thank you all very much !!!