You have any idea what's built up inside the tubes?
Are they 100% steel, or mixed brass/steel?
In general, draino will turn organics, oils, grease, etc. into something water soluble and should be safe for steel. IMO, it's not a bad place to start...
Draino is not safe for soaking aluminum, brass, bronze, pot metal...
If you think there are hard water deposits, acids will be needed to dissolve. Vinegar is a safe place to start but...
It will be difficult to get anything out of them by soaking alone if the orifice/tube diameter is small. You have a small wire you can use to mechanically clean them?
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