This is what a bubbler humidifier should look like when properly functioned and properly hooked up to your oxygen concentrator. To validate that you're getting oxygen through your line, all you need to do is take your nasal cannula, you can put it in a cup of water, and you can see it bubbling. As long as you're bubbling, you're getting air through your oxygen line. You want to confirm that both your cap and your connection hose is screwed on tight and not cross-gritted on your bubbler humidifier. This is an example of an overfilled water bottle, which will push water droplets through your oxygen line. A properly filled bubble humidifier, you want to be filled about halfway full between this minimum and maximum line. When you're putting your bubble and humidifier together, make sure your connections are snug and not over tight, so not to create a crack anywhere on this cap. As a reminder, you want to use distilled bottled water only in your bubble humidifier. As you can see, these holes get occluded when not using distilled bottled water. And this is an example of a cross-threaded cap on a bubbler humidifier. Due to the cross-threading, you can validate that there's no air coming out of the tubing. You can validate this by no bubbles in the water.