I’ve done a lot of research into this topic, and surprisingly, I’ve never heard this advice from a vocal professional before – probably my oversight.
The most common advice is to stay hydrated by drinking water. Some people add a touch of lemon to the water, ostensibly to help cut through mucus, and mucus will definitely build, especially if you have allergies or eat dairy.
The interesting thing is that it seems that you really can’t drink anything to cleanse your chords directly. This is because when you swallow, a flap of skin covers the chords, protecting them. The best way to clean your chords directly is to breathe mist, either from a humidifier or steam from hot water, as in the shower (maybe that’s why everyone sounds better in the shower ).
I tried the shower method and was surprised and excited by the results. I turned up the heat to a barely bearable temperature, then rolled up my fist, placed it over my mouth like a tube, then while positioned near the streaming water, I began to inhale for about ten breaths. Then, I cleared my throat. Later, while practicing, I did not have any of the usual vocal obstacles I often encounter: for some reason, as I rise in pitch, my chords sometimes produce a sound that is almost like a playing card flickering in bicycle spokes. After the shower experiment, my chords were clear, and I experienced one of the best practice sessions I can remember.
I purchased a portable humidifier to use prior to performances. I’ll let you know how it works out.
Anyway, just passing along some info.