Quick answer: Buy a 4-inch gravity floor drain for a lined koi pond. Pick an aerated lid if the pond is deep or heavily stocked. Use the Atlantic-OASE skimmer kit only when that pond already uses one of their listed Pro Series skimmers.
A 4-inch gravity floor drain is the first pick for a lined koi pond. This page is a spec comparison of five currently sold floor drains.
Our research team compared published specs from EasyPro, Aquadyne, DreamPond, and Atlantic-OASE and used one selection rule. A drain had to be on sale now, with construction plus a pipe size or named skimmer on its maker page.
The Floor-First Rule decides every model on this page.
We included a drain only when all three points were true:
- It is sold now as a pond-floor intake, or as a kit that ties a floor intake to a named skimmer.
- The maker’s own product page names the construction or the kit role.
- That same page lists a pipe size or a named compatible skimmer.
We left out filter-housing drain kits, stainless commercial drains with no current home-pond page, and stand-alone pumps or aerators with no floor body.
EasyPro’s BDK3A kit page states a depth note we kept. Ponds that are over 2 feet deep can become stagnant without a bottom drain. That sentence is EasyPro’s claim, not a field trial of ours.
A floor drain still sits inside a full koi fish care plan. It moves settled waste. It does not replace feeding, water checks, or a filter.
Top 7 Bottom drain for koi pond
The picks below are the 7 bottom drains for koi pond on sale right now, listed with what each suits best and an honest drawback. Any comparison table above comes from maker specifications and may cover different models.
1. Heavy Duty Pond Sump Bottom Drain with Dome
Best for: First gravity-fed liner ponds
This listing is a gravity pond sump with a dome lid. Retail copy describes an adjustable lid, a liner collar, and a kit meant for a new floor run into a gravity filter. Owners treat it as a basic intake for a pond that is still being built, not a drain you drop onto a finished liner.
Pros: Adjustable dome lid; Liner collar included Cons: Must install during construction
2. Koi Toilet I Aerated Bottom Drain
Best for: Heavily stocked aerated koi builds
DreamPond’s Koi Toilet I is the aerated model in that line. The maker page lists a slanted air dome, a disk diffuser, and an internal check valve so pond water stays out of the air line. Owners who pay this $335 tier are buying that air hardware with the drain; the compressor is still sold separately.
Pros: Built-in disk diffuser; Premium aerated floor body Cons: Priciest drain on list
3. EasyPro EBD4A 4" Heavy Duty Bottom Drain With Air Diffuser
Best for: 4-inch lined ponds needing airflow
EasyPro’s EBD4A page lists a 4-inch roto-molded body, a welded FPT inlet, and an air diffuser in the dome lid. That same page sets recommended airflow at 0.5 to 1.5 cfm through a 1/2-inch tubing adapter. Owners pick this mid-premium body when they want a named brand and a published air number on a 4-inch Schedule 40 run.
Pros: Published airflow band; 4-inch Schedule 40 body Cons: Air pump sold separately
4. Dreampond Koi Toilet II Bottom Drain 4" w/ Dome
Best for: Concrete or liner, no aeration
DreamPond calls Toilet II the simple 4-inch gravity drain. The maker page lists injection-molded ABS, a thick flange and liner ring, and a glue-up to a 4-inch Schedule 40 elbow or coupling. Owners buy the $95 dome version when they already run air elsewhere and only need a floor intake.
Pros: Lowest price here; 4-inch Schedule 40 fit Cons: No air hardware included
5. AQUADYNE Rhino Retro 2" Bottom Drain
Best for: Small retrofits on 2-inch pumps
Aquadyne sells the Rhino Retro as an over-the-liner drain for ponds that cannot take underground pipe. The maker page says you fill the ballast, attach a 2-inch suction hose or rigid line to the side port, and set it at the low point. Owners use this when the liner is already in and they will not cut a new floor flange.
Pros: Over-liner retrofit body; 2-inch side suction port Cons: Requires a suction pump
6. Rhino Retro 3" Bottom Drain
Best for: Larger retrofits on 3-inch pumps
The 3-inch Rhino Retro keeps the same ballast-and-suction layout as the 2-inch unit, with a wider side port. Aquadyne’s page lists this body at $280 and still describes moving it to shallow water in winter. Owners step up to 3-inch when the pump line is already 3-inch and they want less restriction on a finished pond.
Pros: Wider 3-inch suction port; Over-liner, no trench Cons: Costs more than 2-inch
7. Koi Camp Aquariology Aquarium Drain Fitting
Best for: Quarantine tanks with 3-inch pipe
This SKU is an aquarium drain fitting, not a pond-floor sump. The listing calls it an inline vertical 3-inch PVC strainer with machine-fit Rhino attachments and no gap filling. Owners who already plumb a tank or quarantine vat buy the fitting; it is the wrong shape for a new lined koi pond.
Pros: 3-inch vertical PVC fitting; Machine-fit Rhino joints Cons: Not a pond-floor sump
Comparison: Bottom drain for koi pond at a Glance
Want to browse every option? See the full range of bottom drain for koi pond on Amazon →
Five drains compared by published attributes
These five models met the Floor-First Rule, and the table uses only attributes the makers list.
Our research team counted outlets on those five pages. Three list a 4-inch gravity body, one lists a 3-inch body, and one is a skimmer kit with no floor-pipe size on the Atlantic-OASE page.
| Model | Pipe or connection | Body | Air hardware | Liner or mount hardware | Maker-listed weight |
|---|---|---|---|---|---|
| EasyPro EBD4A | 4-inch schedule 40 PVC | Roto-molded | 1/2-inch tubing; 0.5–1.5 cfm | 16 stainless screws | 12 lb |
| EasyPro BDA | 3-inch schedule 40 PVC | Not named | 10-inch rubber diffuser; 1/2-inch barb | Dual gaskets; 6 stainless screws | 5 lb |
| Aquadyne Rhino II RH2-A | 4-inch | Schedule 80 PVC, hand-welded | 12-inch diffuser; 1.5-inch check valve | Thick flange and liner ring | Not listed |
| DreamPond KOITOILET II 4-inch dome | 4-inch schedule 40 PVC | Injection-molded ABS | None listed | Thick flange and liner ring | Not listed |
| Atlantic-OASE 74017 (formerly BD2000) | Ties to three listed skimmers | Skimmer kit | None listed | Skimmer accessory | 2 lb boxed |
Read the table as a match tool, not a ranking. A 4-inch EasyPro or DreamPond body fits a new lined pond. The Aquadyne Rhino II RH2-A fits a builder who wants welded Schedule 80 PVC.
The Atlantic-OASE kit fits only the three skimmers named on that store page and is not a stand-alone 4-inch gravity floor.
Comparing EasyPro’s own pages, the EBD4A lists 12 lb and 16 stainless screws. The BDA lists 5 lb and 6 stainless screws. That is a 7 lb gap and 10 extra screws on the 4-inch ring.
Aquadyne’s Rhino II page lists a retail price of $798.00 for RH2-A. DreamPond’s KOITOILET II page lists $96.00. Those are maker list figures, not street prices.
Atlantic-OASE’s store page lists a 1-year warranty and a 2 lb boxed weight. None of the other four maker pages we used states a warranty term.
Which pipe size to choose
Pipe size is the first hardware choice, not brand.
Use this list when you pick an outlet:
- Choose 4-inch schedule 40 PVC for the common gravity floor size. EasyPro’s EBD4A page, DreamPond’s KOITOILET II page, and Aquadyne’s Rhino II page all list a 4-inch body.
- Choose 3-inch schedule 40 PVC when the run is short and the pond is small. EasyPro’s BDA page lists 3-inch schedule 40 fittings and pipe.
- Choose the Atlantic-OASE kit only when you already own a matching skimmer. That store page names three skimmers and does not list a floor-pipe size.
EasyPro’s EBD4A page also names two adapters. Use a 4-inch male adapter (MA40) for 4-inch pipe, or a reducing male adapter (RMA4030) to join that drain to 3-inch pipe.
EasyPro’s BDK3A kit page is the 3-inch kit path for the EBD4A body. That kit includes the EBD4A drain, a bulkhead, a valve, and fittings. EasyPro recommends it for Pro-Series PS2 style, PSMEX, or Axiom PSA9000 and PSA11000 skimmers.
Do not step a long gravity run down just to save fittings. The Atlantic-OASE kit is a skimmer add-on, not a substitute for a 4-inch gravity floor on a new koi build.
An above-ground koi pond still needs a true low point. A raised wall does not help if the floor is flat. Slope the floor toward the drain before you set the liner.
Aerated lids versus plain lids
An aerated lid adds air at the drain and does not change the pipe size.
Use this list when you decide on air:
- EasyPro’s EBD4A page lists a 1/2-inch tubing adapter and 0.5 to 1.5 cfm through the diffuser.
- EasyPro’s BDA page lists a 10-inch rubber air diffuser and a 1/2-inch barbed inlet.
- Aquadyne’s Rhino II page lists a 12-inch diffuser and a 1.5-inch commercial air check valve.
- DreamPond’s KOITOILET II page lists no air diffuser.
- Atlantic-OASE’s 74017 page lists no air hardware.
Aquadyne’s page also lists RH2-O, a 4-inch Rhino II with no air diffuser, at a $719.00 retail price as the plain-lid twin of RH2-A.
Pick air when the pond is deeper than 2 feet, or when stocking is heavy. EasyPro’s BDK3A page is the source of that 2-foot stagnant-water note. Pick a plain lid when you already run a separate air system.
Size the air pump to the maker’s number, not to a guess. EasyPro’s EBD4A range is 0.5 to 1.5 cfm, so stay inside that band if you buy that model.
Match the drain to the pond you already have
The pond you have now sets the drain, not a wish list.
Use this match list:
- New lined koi pond with a 4-inch gravity plan: EasyPro EBD4A or DreamPond KOITOILET II 4-inch dome.
- New lined pond that needs floor air and a welded Schedule 80 body: Aquadyne Rhino II RH2-A.
- Small lined pond already plumbed in 3-inch schedule 40: EasyPro BDA.
- Pond that already uses an Atlantic-OASE skimmer with a 6-inch, 9-inch, or 14-inch weir: Atlantic-OASE 74017.
Atlantic-OASE’s store page names the three skimmers by model number and flow:
- 6-inch weir, 4600 GPH, model 74040
- 9-inch weir, 7000 GPH, model 74041
- 14-inch weir, 15000 GPH, model 74037
If your skimmer is not one of those three, do not force this kit; buy a floor drain that matches your pipe instead.
Aquadyne’s Rhino II page stresses a 3-inch height over the discharge port. That extra cover is for concrete over the horizontal pipe. It matters on a poured floor, and less on a thin liner dish with no slab.
DreamPond’s KOITOILET II page says the drain fits a 4-inch schedule 40 PVC elbow or coupling. That is a simple glue-up, not a welded Schedule 80 body.
Two low spots need two drains. Maker pages we read do not publish a drain-count-by-gallon chart. Place each drain at a low point.
Install notes taken from the maker pages
A bottom drain goes in before the liner, not after the fish.
EasyPro’s BDK3A page describes the under-liner path in plain steps:
- Set the drain base under the liner at the low point.
- Run flex PVC from the drain to the skimmer box.
- Fit the bulkhead in the skimmer.
- Join the flex PVC to that bulkhead with a PVC male adapter.
- Put the valve inside the skimmer to split top flow and bottom flow.
EasyPro’s EBD4A page adds hardware details for the 4-inch body. The inlet is a welded FPT thread, so you do not need a rubber coupling. Air tubing can sit under the liner and rise through the center stand pipe into the dome lid.
Aquadyne’s Rhino II page says a bottom drain is the first thing installed in a pond. All joints are hand welded. The air line enters the air bladder by a direct pipe, not a line snaked through the water pipe.
The 1.5-inch check valve keeps water out of the air line. DreamPond’s KOITOILET II page says the drain works for liner and concrete installs with a 4-inch schedule 40 elbow or coupling.
Atlantic-OASE’s 74017 page is a skimmer accessory page. Install it only with the three named skimmers. Follow the maker’s kit manual for hole size and fittings.
Do not glue a gravity line with sags that trap solids. Keep the run short and downhill, and support the pipe so the liner cannot pull the flange.
Leave the dome on once fish go in, and do not run the pond with the lid off.
Care after the drain is in
A floor drain fails when the pipe clogs, not when the plastic looks old.
Add these checks to your pond maintenance schedule:
- Confirm water is moving at the drain, not only at the skimmer weir.
- Open the skimmer valve and compare top flow to bottom flow if you have a kit like EasyPro BDK3A.
- Clear the dome or strainer so leaves cannot seal the opening.
- If the drain is aerated, confirm bubbles still rise at the lid.
- Keep the air pump above water level so the line cannot back-siphon.
EasyPro’s BDK3A page says the included valve controls how much water enters through the top and bottom inlets. Use that valve, and do not leave the floor line wide open if the skimmer weir then starves.
Aquadyne’s Rhino II page lists the 1.5-inch check valve as the guard against water in the air line. If bubbles stop on an RH2-A, check that valve and the air pump before you blame the drain body.
Settled waste should go to the filter, not stay in a sump under the dome. If the floor stays black after weeks of flow, the low point is wrong or the pipe is blocked. Fix the slope or the pipe.
FAQ
Do I need a bottom drain if the pond is under 2 feet deep?
EasyPro’s BDK3A page flags ponds over 2 feet as the stagnant-water case. A shallower pond can still use a drain if waste piles at one low point. If you already plan a gravity filter, a 3-inch EasyPro BDA is the smaller-pipe option we compared.
Can I add a floor drain after the liner is in?
The EasyPro and DreamPond pages we read describe new installs under or through the liner. They are not retrofit kits for a finished, full pond. The Atlantic-OASE 74017 kit ties to an existing named skimmer, but you still need a floor intake and a pipe run.
How much air should an aerated drain use?
EasyPro’s EBD4A page is the only page in this set that publishes a flow band. That band is 0.5 to 1.5 cfm through the diffuser. EasyPro’s BDA page lists a 10-inch rubber diffuser and a 1/2-inch barb, but no cfm number.
Is a 3-inch drain enough for koi?
EasyPro’s BDA page lists 3-inch schedule 40 pipe, so yes, a 3-inch body is a real current product. It is not the default we use for a new lined koi pond. Use 3-inch when the plumbing is already 3-inch, or when EasyPro’s BDK3A kit path matches your skimmer list.
What is the difference between a floor drain and a skimmer drain kit?
A floor drain is a body in the pond floor with its own pipe. EasyPro EBD4A, EasyPro BDA, Aquadyne Rhino II RH2-A, and DreamPond KOITOILET II are floor bodies. The Atlantic-OASE 74017 kit is a skimmer accessory that lets a listed skimmer pull from the floor and the surface at once.
How many bottom drains does one pond need?
None of the five maker pages we used publishes a drains-per-gallon chart. Use one drain at the single lowest point. Use a second drain, on its own pipe, only if the floor has a second low point.
Does a bottom drain replace a skimmer?
No. A floor drain takes waste that has already sunk, and a skimmer takes floating leaves and film. Atlantic-OASE’s 74017 page and EasyPro’s BDK3A page both describe that split, so keep both paths open unless you are flushing one line.
