How does the Recycle Bin work?
When you delete a file from a hard drive the file is moved to a folder named
$Recycle.Bin on the same drive. So when you delete the file
D:\Work_Files\SuperWeirdPr0n.mp4 it's actually moved to
D:\$Recycle.Bin. The main Recycle Bin "folder" is actually just the aggregation of the content from all
$Recycle.Bin folders from all the disks you have available.
How does that apply to TrueCrypt volumes?
Well, pretty much the same. When you send a file from a mounted encrypted volume to the Recycle Bin, it won't leave the encrypted volume and it will stay "safe".
If it makes you feel better, just use Shift + Del.
Can your files be recovered by a 3rd-party?
Yes. Regardless of your Recycle Bin situation, it's highly likely that there's still some evidence of the files existence somewhere and enough information to recover it. When you open files inside an encrypted volume, most programs will happily cache it somewhere else in an unencrypted format.
For more information on that, please check both answers in this question.