The issue is pressure buildup. You fermenting and generating more CO2 than can escape the capacity of your valve. You could take the plug out, remove the cable from the plug, put a tube in so it isn’t into the brew liquid, and put the other end in a bucket of water so the end is always under water. Here’s an example, I just got this off the Internet because I didn’t have any pictures from doing this myself, but I’ve done this.

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