Amber dropper bottle cleanup

Hi all,
I'm a newbie at this chem lab prep in a high school, and have been trying to find all the empty/dried up dropper bottles and refill or re-use them for other chemicals where necessary.
So...this may be a daft question, but better to ask than assume, and do the wrong thing. All the lab manuals mention cleanup of the glassware used in the practicals etc but I haven't found anything regarding the chem dropper bottles.

*Is* it possible to clean them out thoroughly?
The previous lab prep guy had left a lot of them soaking in what I assume was just soapy water... after rinsing them out in hot water and attempting to clean the insides with a test tube brush, there's still some residue left, especially just in the 'shoulder' area of the bottles.
Is there really good way to get rid of that across the board, or is it a case of soaking them in whatever is correct for the original chemical that was in it first?

I would greatly appreciate some tips with this.
Thank you
It is typically possible to clean them but there is no panacea treatment, some will require different methods depending on what the droppers have been used for unfortunately.
As SAK said basically. Don't worry because with time and experience you will know:

1) Whether it's worth cleaning in the first place and just re-using it for that chemical only.
2) What chemical/solvent to use to clean it

If there is a tough stain I need to get off but don't know what it is/too lazy to look it up, I just make a small amount of aqua regia/piranha solution which always does the trick. Bear in mind these are very corrosive and dangerous solutions to handle so don't go down that route until you know exactly what you are doing and feel confident in doing it.
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Peter Sigsworth

From my own experience and a quick trawl through colleagues' posts on here:

Worth trying different ones if your first attempt fails:

Permanganate staining plastic aspirators or glassware? Add a teaspoon full of glucose and 1M HCl or Sulfuric acid. Also, could try 50ml of 20 vol hydrogen peroxide to 50ml of 2M sulphuric acid.

For removing iron III stains - oxalic (ethanedioic) acid solution 1/2M.... works well for iron filings stains in sinks. Works well for general stains too

Copper and copper oxide stains - you could try concentrated nitric acid. Also used to clean copper off carbon electrodes Do in fume cupboard

oil/cooking oil/grease/vaseline – acetone, white spirit or ethanol

lime water white stains on plastic/glassware– 1M HCl

Methylene blue – soak in dilute yeast solution overnight or IDA and a small amount of HCl

Iodine (or any Halogen) Sodium Thiosulfate solution 1M

General stains -conc/strong acids Sulfuric or Nitric (fume cupboard)
If they are the little bottles I'd try hot water and detergent first, if you have an ultrasonic bath try putting a few bottles at a time in it.
They've got the hot regular wash treatment...and then I believe the last tech had them in some vinegar as well... most have come out pretty clean, but some just have some stubborn whitish residues, and of those, some have lost their labels in the soaking I don't know what was in them originally. Sadly, we don't have an ultrasonic bath.