Best Overflow Boxes for Sump Systems
A sump dramatically increases water volume, hides equipment and improves filtration, but getting water from the display tank down to the sump requires a reliable overflow. Choosing the best overflow box sump aquarium hobbyists can depend on means evaluating noise, flow capacity and fail-safe design. Gensou Aquascaping at 5 Everton Park, Singapore, has plumbed sump systems on everything from nano reefs to 6-foot monster tanks over more than 20 years. The overflow is the one component you cannot afford to get wrong.
Internal Weir Overflows
An internal weir is a box built into the tank with holes drilled through the bottom glass or back panel for drain pipes. This is the most reliable overflow design because it involves no siphon and cannot lose prime. Water simply spills over the weir edge and falls by gravity into the sump below. Most new reef-ready tanks come with internal overflows pre-installed. If you are ordering a custom tank in Singapore, request a corner overflow or a coast-to-coast overflow along the back wall. Corner overflows are compact but can create dead spots; coast-to-coast designs provide superior surface skimming across the entire tank length.
Hang-On-Back Overflow Boxes
For tanks without drilled holes, a hang-on-back (HOB) overflow box uses a U-tube siphon or a weir-and-pump mechanism to transfer water over the tank rim and down to the sump. The CPR CS90 and Eshopps PF series are widely used. HOB overflows cost $80-200 and install without drilling, making them attractive for renters or hobbyists unwilling to modify their tank. The critical weakness is siphon reliability: if the U-tube loses its siphon during a power outage and does not restart, the return pump will overfill the display tank. Always pair a HOB overflow with an anti-siphon valve on the return line.
Eshopps Overflow Boxes
Eshopps produces some of the most popular HOB overflow boxes for good reason. The PF-800 handles up to 800 gallons per hour (roughly 3,000 litres per hour) and fits tanks with rims up to 16 mm thick. The dual-drain design allows a Herbie or Bean Animal drain configuration for near-silent operation. Construction is durable acrylic with smooth edges and reliable suction cups. In Singapore, Eshopps overflows are stocked by several reef equipment dealers and typically run $120-180. The included plumbing fittings save additional trips to the hardware store.
Synergy Reef Shadow Overflow
For a sleek, low-profile internal option, the Synergy Reef Shadow Overflow mounts inside the tank with a minimal footprint. Its slim design takes up far less space than a traditional corner weir, leaving more room for aquascaping. The ghost overflow version is made from dark-tinted acrylic that virtually disappears against a black background. Flow capacity suits tanks up to 400-500 litres. Installation requires drilling the tank bottom, which is best left to a professional glazier experienced with tempered versus non-tempered glass panels. Price ranges from $200-350 depending on the model and drain configuration.
Drain Configurations: Durso, Herbie and Bean Animal
How you configure the drain pipes inside the overflow box determines noise levels. A single Durso standpipe is the simplest setup: it reduces gurgling by allowing air to enter the drain pipe gradually. Effective but not silent. A Herbie drain uses two pipes, one fully submerged (primary) and one as an emergency backup, achieving near-silent operation when tuned correctly. The Bean Animal method adds a third pipe for an open-channel emergency drain, providing maximum redundancy. For apartments and condos in Singapore where noise travels through thin walls, a Herbie or Bean Animal setup is strongly recommended.
Sizing Your Overflow for the Return Pump
The overflow must handle more flow than the return pump delivers to prevent flooding. Calculate your return pump’s output at the head height it needs to push water, not its maximum rated flow. A pump rated at 3,000 litres per hour may only deliver 2,000 litres per hour after accounting for head pressure and plumbing friction. Choose an overflow rated for at least 1.5 times this actual flow rate. Undersized overflows create a constant battle between inflow and drainage, leading to fluctuating water levels, noise and potential disaster if the overflow cannot keep pace during a blockage.
Installation Tips for Singapore Setups
If drilling your tank, always drill the bottom panel rather than the side or back for the strongest gravity drain. Use bulkheads with silicone gaskets rated for aquarium use. In HDB flats, position the sump cabinet on a waterproof tray or mat to protect laminate flooring from minor drips. Route drain pipes with minimal bends to maintain flow and reduce noise. Gate valves on drain lines provide fine-tuning control for Herbie configurations. Test the entire system with plain water for 24 hours before adding livestock, checking for leaks at every joint and confirming the overflow handles full return pump flow without surging.
Maintaining Your Overflow Long Term
Algae and calcium deposits accumulate inside overflow boxes and drain pipes over time, gradually reducing flow capacity. Clean the overflow chamber monthly with an algae scraper and flush the drain pipes quarterly with a vinegar solution to dissolve mineral buildup. Check the emergency drain pipe remains clear and unobstructed at all times, as it is your last line of defence against flooding. For HOB overflows, inspect the U-tube siphon weekly and ensure the best overflow box sump installation remains secure against the tank rim. A small investment in regular maintenance prevents the catastrophic failures that give sump systems an undeserved reputation for flooding.
Related Reading
emilynakatani
Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
