How to Plumb an Internal Overflow Tank — Step by Step

Got a brand new tank, a bag of parts, and no idea where to start? You're not alone — plumbing an internal overflow tank is one of the most common questions we get at Nature Aquariums. In this video, Henry walks you through the entire process step by step, from understanding your bulkhead hardware all the way to siphon breaks and return line setup. This is how we do it every day on real customer installs.

Understanding Your Plumbing Kit

Most internal overflow tanks — Aqueon, Marineland, Planet Aquariums — come with a plumbing kit, or you can buy one separately. The key component is the bulkhead: a fitting that seals into the drilled hole in your tank using a rubber gasket and a threaded nut. Tighten it down, and it creates a watertight seal that your pipes connect to.

Bulkheads come in different sizes based on the hole diameter (1/2", 3/4", 1", 2") and the pipe size they accept. If you're not sure what size you need, trace the hole onto cardboard and bring it to the store — easiest way to get the right fit.

The bottom fitting on your bulkhead will be one of three styles:

Barbed — for flexible hose; use a clamp to secure
Smooth — for rigid PVC; use primer and solvent glue (permanent)
Threaded — use Teflon tape or thread sealant; removable later

Tools & Supplies You'll Need

Bulkhead wrench — use the short one that comes with the kit, NOT a large pipe wrench. Too much torque will crack the glass or the bulkhead.
Silicone lubricant (food grade) — not silicone sealant. Apply to the rubber O-ring/gasket before install. This creates a proper watertight seal against the glass. Also use it on barbed fittings to help hoses slide on cleanly.
PVC cutter — most kits include a 30" pipe; you'll need to trim it to match your tank height.
Rag — to clean and protect your hands around unfinished cut glass edges. Do not use bare fingers — the glass edges are sharp and unfinished.
Razor blade — for used tanks with salt or calcium buildup around the holes. Scrape clean before installing or you won't get a good seal.

Drains, Returns & Vents — Know the Difference

The weir is the overflow box inside the tank that keeps fish and large debris out of your plumbing. The water level inside the weir determines where your drain line sits.

Drain — the larger hole; water flows from the weir down through here into your sump or wet dry.
Vent — critical and often overlooked. Without it, your drain will gurgle like a toilet because it can't get enough air. Always install the vent.
Return — the smaller hole; this is where water pumps back up from your sump into the display tank via flexible return lines.

Adjusting Drain Height to Reduce Noise

The height of your drain standpipe directly affects how loud your tank is. The lower the drain sits, the farther water falls before hitting the sump — more noise. Raise the drain as high as possible (just below the tank rim or glass lid) so the waterfall drop is minimal. If your kit has an adjustable drain, use it. If it's fixed PVC, measure and cut to the correct height before installing.

Siphon Break & Check Valve — Don't Skip This

When power goes out, water will back-siphon through your return lines and drain into your sump — potentially causing an overflow. You have two ways to prevent this:

Check valve — installed on top of the return pump; automatically stops back-flow when power cuts.
Siphon break — a small hole drilled at the top corner of your return elbow. It lets air in when the pump stops, breaking the siphon. A little water will drip from it while the pump runs — that's normal and expected.

If your return lines point downward into the tank and you have neither a check valve nor a siphon break, you risk overflowing your sump every time the power goes out. Don't skip this step.

Pro Installation Tips

Work with the tank pulled away from the wall if possible — you'll have much better access to tighten bulkheads underneath.
Use the pipe itself to hold the bulkhead in place while you tighten the nut from below — much easier than reaching blind.
Tighten until it resists and the wrench slips — that's by design. Don't overtighten.
If you see a drip after tightening, the bulkhead is likely not centered. Loosen it, reposition slightly, and retighten. Don't add Teflon tape or extra silicone — it's a seating issue, not a sealant issue.
If you still have a leak, pull the bulkhead, clean the gasket completely (even one grain of sand will cause a leak), reapply silicone lubricant, and reinstall.

Video Chapters

0:00 — Introduction: plumbing a brand new overflow tank
0:15 — Overview: Aqueon, Marineland & Planet Aquariums kits
1:00 — Bulkhead explained: how it works, sizes, and what fits
2:30 — Three fitting styles: barbed, smooth, and threaded
3:30 — Tools you need: bulkhead wrench, silicone lubricant, PVC cutter
5:00 — Prepping the glass: cleaning, razoring, protecting your hands
6:00 — Weir, drain, vent, and return — nomenclature explained
8:00 — Siphon break vs. check valve — how to prevent back-siphon overflow
9:30 — Adjustable drain height: why it matters for tank noise
11:00 — Marking and cutting PVC to the correct height
12:00 — Installing the bulkhead: step-by-step with pro tips
14:00 — Troubleshooting drips: centering the bulkhead, cleaning the gasket
15:30 — Wrap-up and final tips

Bottom Line

Plumbing an internal overflow tank looks intimidating but it's very manageable when you understand the parts and follow the right steps. Use the right wrench, lube your gaskets, get your drain height correct, and always install a siphon break or check valve. Do it right once and you won't have to touch it again.

We carry plumbing kits, bulkheads, silicone lubricant, and everything else you need at natureaquariums.com — shipped right to your door.