The silicone tubing I've used is super soft, like the same texture as the stuff they tie around your arm when the doctor is taking blood. I would not use it in the way want to.
I use a bubble counter to get that visual representation. Specifically
this one, but there are other sellers out there that can get this style to you quicker.
Not sure if you were planning for this or not, but you also need a check valve to keep your regulator from filling with water.
And unless you are using a diffuser or something just pumping co2 into a hob isn't going to do much to increase co2 levels as it will outgas immediately.