Thanks for clarifying this. When I realized my mistake, I switched to doing things as you advised and put the entire container into a larger one.It depends on where you are starting from. The device is made for people who are very sick. You had misinterpreted my advice, just put the device as-is in a larger container and cover loosely with a kitchen towel, and the mouthpiece sticking out. Now you are NOT increasing the water-created resistance, but you ARE increasing the CO2 you are building up in the reservoir with each exhale, and that makes it much more productive WHEN YOU ARE READY for this.
I would say around CP25.
BTW, as far as CP, you should do everything you can to get your CP to 25. I have found most people will stop there, and they get a lot of benefit (which continues for the forseeable future even if you stop the exercises.) But if you go further, you will need techniques like this one, and the next stop is CP33 or so. Few get byond that, sometimes to CP40. My CP is 40 or 45 part of the year, dropping back in winter to 38 or 40.
Getting to 60 takes another dose of commitment which I've never been up for. Maybe there will be other avenues to get there.
But they do talk about varying the amount of water in the device in the frolov manual. http://www.aviva.ca/files/pdfs/frolov-manual.pdf And they talk specifically about increasing the water 1 ml every 3-4 days. As well as good charts on increasing all the variables as you progress. They said, "For example, if respiration with 20 ml of water in the simulator inhaler causes complicated breathing or strong resistance to breathing, you should not increase the water volume. Then, if after 3-5 days of training this water volume does not cause the sensation of complicated breathing, you can increase the water volume by 1 ml." I adjusted the water each time that I used the breathslim so that I didn't have strong resistance, just a very slight resistance.
When my CP dropped dramatically, I realized I was not ready for the larger container and have mostly taken a break from the breathslim. I've had a lot of stress in my life recently. My plan is to go back to regularly using the breathslim in the summer, which is a much stronger time of year for me.