If you have a drain near by or if you don't mind a garden hose, you can add one more bulkhead for water changes. Put it 30%-ish of the way down from the waters surface (depending on your average water change volume). Lowes and HD sells a pvc to garden hose adapters in the plumbing isle. When it comes time to do a water change, you just roll out the hose, open the valve, and let it drain to the height determined by the bulkhead.

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