It is a threaded fitting that whiantegelbw is talking about they give you a few different sizes to match your plumbing. They are a slip fitting on the pump side.
The only downsides to not gluing it is being able to change size or if you stripped the threads.
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Brian
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220g inwall 48"x36"x30"
110g mangrove refug/sump
Poison Dart Frog Vivarium
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