Most pods will have a hole covered with an attached rubber cover.
Usually, this will be the fill port where one inserts a needle pointed e-juice bottle to fill the pod. The rubber cover will also act as a grommet to plug the hole once you refill the pod. These appear similar to bungs as on wooden casks.
Brief aside here. Yes, there is an actual thing called a bunghole. It is the hole in a wooden cask. The covering of it was done at times with beeswax. Sailors, supply men would often use wooden mallets to whack the wax in place. This gave off a sound of "bung" if the cask was filled. This is how bungs and bungholes then became known as such.
There are various such ports on RTA or tanks as well. A lot of more modern/current tanks are using top fill means to refill. If we knew which tank you're using we might aid in capacity of defining where and how you refill the tank. You may need to consult its use manual which should have come with it, or possibly a Youtube
video.
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