First off, you need to completely field-strip them down to pieces.
Now, the plastic
tanks and o-rings are a different matter. I would NOT soak them in Everclear (or ANY strong alcohol) for longer than 30 or 60 minutes. Plastics and rubber can be harmed by prolonged exposure to alcohol.
So take a cup or bowl, put a cup of water in it, and about half a dozen drops of dishwashing liquid in it, and get it good and mixed up. Then soak the plastic and rubber bits in that overnight. Then rinse the HECK out of them to get any soap or perfume residue off them.
IF that doesn't work, go to a homebrewing supply store and get some "B-Brite" or "1-Step". These are powdered "oxidizing cleansers" used to clean and sterilize brewing equipment and will clean almost ANY smell, taste or stain from plastic or glass safely, they rinse off easily, and leave no residue . Instructions for use should be on the container...
Good luck. If all else fails, the plastic and rubber parts that might hold funky smells or tastes are replaceable, and can be bought for next to nothing, so you could just get new parts. I know that is a pain, since you thought you were getting useable parts in an classifieds sale, and now you might have to spend extra money to get them going, but, as they say, "Caveat Emptor"...
Sorry you had a bad experience in the Classifieds. I've made about 8 or 10 purchse through the ECF classies--from
mods to super-high-end
tank systems--and I've been lucky. All my sellers were 100% top-notch people, who provided great communication, and sent me clean, fully-functional gear for great prices. Better luck with the Classies in the future, man...