Plumbing is able to pass through aquarium or filter panels with a fitting called a bulkhead. It consists of three parts including the main body, gasket and nut. A hole is cut in the panel so the bulkhead can be inserted and sealed by the gasket and nut.
They are sized by standard pipe sizes and can have either slip (glued) or threaded fittings. Add them to your system in a way that they can be removed easily if they begin leaking. (ex. Union Fittings)