Fellow textbook and technical manual keeper here! A few years ago I donated some to my library. Don't know if they put them out for sale. I still have a lot more stored on the floor in my house.
Was it a struggle for you to finally donate some? Most of my books were technical in nature, and many were out of date. My reluctance to get rid of them was a combination of sunk cost fallacy (those suckers cost me ~$100/each on average), the feeling that I was tossing some good resources for useful information that me or my kids might make use of some day (but duh, we could find better/more up to date information on these topics online or from a library), and sheer sentimentality (I am oddly sentimental about the weirdest stuff).
I tried selling some -- no dice. I briefly considered burning them ala a Viking funeral pyre. But I finally decided that at least there is a small chance someone will want one of the books, so now they're the library's problem to deal with.
I like the Viking funeral pyre idea! But I won't do it myself.
Yes, it was a struggle to donate them, but I viewed as a self-improvement thing,
like going to that party even though you are shy, since you'll be glad you did afterwards. 'Doing the right thing' even though you don't want to.
My textbooks are 95% free from work days. They allowed me to take them with me when I left. All computer programming stuff.
I keep them for as a reminder of how productive I was in this life. So, sentimentality there, yes. I never read them unless I am thinking of recycling them. Then after a few paragraphs, I say 'I can't discard this priceless stuff. It's the only physical representation I have of my work role in the world'. They are all in one room, and take up only about 20% of the floor space when stacked.
What doesn't help is seeing similar textbooks on Ebay listed for $30 to $40 each. But for some reason, now I can't see if they ever sold or not, and for how much. Has Ebay hidden that information now? I used to be able to see it somewhere, like 'completed auctions', but it has disappeared.
So when I donated them I assumed I was possibly missing out on $30 each! (I know, dreaming).
I did put an ad on Craigslist for them, and suggested buyer make an offer. Zero responses, sadly.
I also have a few stacks of my computer programs in the same room. I have actually recycled about 30% of these, and now am actually regretting it! Who knew? Oh well, I still have a lot. Also saving presentations I made describing the projects I led.
I also had a bunch of those 3 ring binder manual full of training lessons, which I was able to recycle without too much emotion. Pop open the metal rings, toss paper into recycling bag, donate 3 ring binder to Goodwill. They sell them for $1 or $2 each, believe it or not. I actually saw a guy at the cash register buying one once at Goodwill. I don't miss those. Kept a few empty 3-ring binders just in case, lol.