Syncing and capacity issues - how do I fully delete certain iPod items?

Question

Perhaps I just don't know how to properly delete files off my iPod. In short: Podcast items that I manually drag from iTunes to a playlist in my iPod don't seem to fully delete after I delete them from the playlist. And I don't see them listed in my ipod podcast area.
The bulk of my ipod consists of music I manually tossed on there. That portion never gets synced. And I haven't added new music in a long time.
I have three different podcasts programs I auto sync the last 3 episodes of (it was 5, but I reduced it due to the problem I'm describing in this post).
I also manually drag (via iTunes) some podcasts from my laptop to a playlist on the iPod. I do this once a week. The shows I move over aren't always the same, this is one reason I don't auto sync them. (i.e. I might decide to move over a really old episode of a program I rarely listen to.)
The podcasts I manually moved to the playlist seem to only show up in the playlist. They don't appear in the Podcast or Music sections.
Each week I also delete the contents of the playlist (by going into the playlist and deleting the listing of the playlist's contents).
*If I delete the (manually moved) item from the playlist then it appears that it doesn't free up the space*. Since I can't find any other mention of the item on the iPod, how do I delete it?
I'm aware that if I drag an item from iTunes to the iPod's podcast section, then a entry for the item shows up there. And then I can delete the item and get that space back. Maybe this is the proper way to move files and perhaps I'll start doing that. But at this point I just want to fully delete all the old items I can't see anymore.
Because of this problem I've had to delete more and more other items from my iPod to free up space for the new podcasts I want to manually move over. I'm getting tired of doing this. Thus, this post.
If need be I can provide examples of the exact steps I take, space left, etc.
Using iTunes 10.1.2. I've read some threads in the past about capacity issues that started cropping up in 10 or so. I don't know if my problems are related.
Thanks,

Answer 1

Note: by using a third-party iPod file browser, I'm able to easily see all the hidden podcasts (they add up to many many megabytes). However, the one I'm currently using, Senuti (free version) doesn't seem to allow track deletion from its browser, it just lets me transfer from the browser to iTunes.
Is there a (free?) file browser that will let me delete tracks?
Also, I haven't examined all of the hidden tracks, but for two of the podcasts shows, it looks like the oldest hidden ones were added on 6/19/2010. iTunes 9.2 released on 6/16/2010 and I likely installed it around that time.