Here's another drink similar to the tea, and it is what i am using right now as I prep for a German and Japanese TV show. Remember, I am not a doctor or vocal health specialist and the following drink mix is not intended to treat, prevent, or diagnose, any health or vocal health issue that may be related to your specific situation.
Every day right now as I am in training, I simply take a bottle of water, add a few packets of Emergen-C, 10-15 drops of each liquid zinc, liquid Licorice, liquid Slippery Elm, Liquid B-complex and Stevia. After I shake up this mixture I add one packet of X20 (singerswater.com).
You can do an Internet search to discover why I use each of these ingredients. For RYV owners, it's all explained in there too;) I don't use this all the time and I am always trying different combinations. But this one works well. My voice feels amazing, my glass breaking power is at an all time high and the Zep tunes I am singing for the German show are solid...
Oh yeah, I DO do a lot more than just drink this tea. You got to do your exercises every day, including vocal and cardio. In fact, I do an 60-90 minutes on the treadmill in the morning, and during that time, I do lots of lip bubbles and scales and sing some songs;)
Hope this is of some use to someone, just though I'd share:)