> For the complete documentation index, see [llms.txt](https://docs.synergyreef.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.synergyreef.com/installation-manuals/the-synergy-reef-shadow-overflow/drilling-your-aquarium/drilling-return-holes.md).

# Drilling Return Holes

You will need to have return bulkheads in your aquarium for the return pump to flow water back into your aquarium. To drill these you will need the following. 

* [ ] 3/4" SLP X FPT Bulkhead <https://synergyreef.com/product/3-4_bulkhead-fpt-slp/>
* [ ] 35mm Diamond Holesaw Bit <https://synergyreef.com/product/35mm-diamond-holesaw-bit/>

Follow the [Drilling Your Aquarium](/installation-manuals/the-synergy-reef-shadow-overflow/drilling-your-aquarium.md) instructions for the drilling procedure.&#x20;

Where you install them is up to you, but we recommend about 2" below the top of the aquarium.