THANK YOU!It's standard 1/16" ID silicone tubing. I use 1/16" ID x 3/16" OD, though other OD should also work okay.
Amazon, eBay, are reasonable sources.
I'm pretty sure this is what I bought: https://www.amazon.com/Silicone-Tubing-16-ID-Wall/dp/B01LZTH5XR?keywords=1/16"ID+silicone+tubing&qid=1536202377&sr=8-8&ref=mp_s_a_1_8
(I got 10', maybe used 1' to redo multiple bottles [emoji3] )

I’ll order...uh...5’ (I guess) tonight.

I should have just bought that rather than an extra 2 bottles - I don’t even know if I like the mod yet. Lol. Well, Labor Day 15% off sale, so not too bad.