How To Separate Oil from Bilge Water
A dry bilge system removes residual fluid from the low points of a boat. On many vessels, that fluid is not just water. It may carry oil, diesel fuel, hydraulic fluid, or other contaminants picked up from the machinery spaces and compartments where it collected.
That raises an important question: if the Arid Bilge System removes that fluid, where does it go?
For boats kept in the water, moored in a marina, or operating in environmentally sensitive areas, discharge management matters. Eco-Drain is designed to add an environmental protection step by helping separate lighter hydrocarbons from bilge water before separated water is discharged or routed to an approved location.
What Eco-Drain Does
Eco-Drain receives untreated bilge fluid discharged from the Arid Bilge System and gives that fluid a controlled chamber area where lighter hydrocarbons can separate from water.
The goal is simple: reduce hydrocarbon discharge risk, reduce exposure to fines, and support more responsible bilge management.
A traditional bilge pump discharges whatever fluid reaches it. You can get hit with a hefty fine. Eco-Drain gives contaminated bilge fluid a separation step first.
Eco-Drain does not chemically treat the water. It uses chamber-based gravity separation. Because hydrocarbons such as oil, diesel fuel, and hydraulic fluid are lighter than water, they rise above the water layer and remain inside the Eco-Drain chamber until they are removed during service.
In simple terms:
Arid removes the fluid. Eco-Drain separates the hydrocarbons.
Where the Idea Came From
Once the Arid Bilge System proved it could automatically pull residual fluid from low points across a vessel, a second need became clear. Some boats also needed a simple way to manage bilge fluid that might contain oil, diesel fuel, hydraulic fluid, or other hydrocarbon residue before it left the boat.
One of the projects that helped drive this need was Bolder Won, a 75-foot custom catamaran built in 2007. The vessel received an extensive Arid Bilge Systems installation with multiple systems and many bilge zones.
Because those systems could automatically remove and discharge bilge fluid, the project also created the need for a companion product that could help separate hydrocarbons before discharge. Development on the Eco-Drain concept started around 2007.
The approach borrows from large-scale oil-water separation and wastewater-treatment principles. In those systems, contaminated water is given time and chamber space to separate naturally so lighter hydrocarbons rise above the heavier water layer.
Eco-Drain adapts that same basic principle into a compact onboard marine format.
How Eco-Drain Works With the Arid Bilge System
The Arid Bilge System uses controlled pressure and vacuum inside its collection chamber. Raw bilge fluid is pulled from wet zones throughout the vessel and collected inside the Arid system.
- Once fluid is collected, the Arid system enters its discharge cycle
- Without Eco-Drain, that untreated fluid follows the vessel’s normal approved discharge routing
- With Eco-Drain installed, the Arid system discharges untreated bilge fluid into the Eco-Drain first. Eco-Drain then gives the fluid time and chamber space to separate before the separated water continues through the discharge path
Untreated fluid enters through the inlet and flows into the first chamber. Heavier water settles lower in the chamber, while lighter hydrocarbons rise toward the top.
The operating water level is controlled by the relationship between the inlet height, internal transfer piping, and discharge outlet height. As the fluid settles, water from beneath the hydrocarbon layer continues through the unit, while the hydrocarbon layer remains behind in the chamber for removal.
Eco-Drain does not replace the Arid Bilge System. It is an optional companion product installed downstream from the Arid discharge path.
Three Eco-Drain Models
| Model | Recommended Arid Systems | Dimensions | Build |
|---|---|---|---|
| Eco-Drain 1 | Series 1 and Series 2 | 14 x 14 x 10 in | Lexan-type plastic, 1/4 inch thick |
| Eco-Drain 2 | Series 2 and Series 4 | 20 x 18 x 12 in | Mid-size Eco-Drain model with drain valve |
| Eco-Drain 3 Premium | Series 4 and Series 9 | 22 x 20 x 14 in | Aluminum with Awlgrip Matterhorn White finish |
The match is straightforward: choose the Eco-Drain model that fits the Arid system, vessel size, discharge layout, and installation requirements.
None of the Eco-Drain models require power.
Explore Different Models and Options
Why Mounting Height Matters
This is where installations can go wrong, so it is worth being clear.
Eco-Drain has no pump, no vacuum, and no check valve. It does not force fluid out of the unit. The Arid Bilge System discharges under pressure, but Eco-Drain relies on gravity to move separated water through the discharge path.
That means Eco-Drain should be mounted higher than the final discharge point whenever the vessel layout allows.
In most installations, Eco-Drain should be mounted on a shelf or platform secured to the bulkhead. It should not be mounted flat against the bulkhead. The shelf must support the dry weight of the unit plus the added weight of fluid inside the chamber during operation.
The installer also needs to allow enough clearance above the unit to open the hinged lid or service hatch. Space should also be left around the unit for inspection, hydrocarbon removal, cleaning, and future service.
If the boat allows enough height, Eco-Drain may gravity drain directly to an approved discharge point.
If the boat does not allow enough height for direct gravity discharge, Eco-Drain can drain into a shower sump or other approved collection point. The sump can then pump the separated water overboard through the vessel’s existing discharge system.
The key rule is simple:
Eco-Drain does not pump water out. The installation must allow separated water to drain by gravity.
Servicing Eco-Drain
Eco-Drain is passive. It separates hydrocarbons, but it does not remove them automatically.
That is why inspection matters.
Hydrocarbons should be removed before the hydrocarbon layer reaches roughly halfway up the chamber. Do not wait for the chamber to look completely full before servicing it.
If the hydrocarbon layer is allowed to overfill, hydrocarbons can reach the lower transfer pipe or move toward the discharge side. When that happens, separation performance is reduced.
Only the Eco-Drain 2 includes a drain valve. Other Eco-Drain models require hydrocarbons to be removed manually with a baster, suction pump, reversible transfer pump, or similar service tool.
Collected hydrocarbons should be placed in an approved container and taken to a proper disposal location. Do not discharge collected hydrocarbons into the water, storm drains, bilge, marina, or onto the ground. That defeats the purpose of the Eco-Drain product line.
Always follow marina, boatyard, and local environmental disposal requirements.
Cleaning the Eco-Drain Chamber
In normal use, Eco-Drain does not need constant cleaning. However, oil film, organic buildup, or residue may collect on the inside walls or viewing panels over time.
If the viewing panel becomes cloudy or difficult to see through, the unit should be cleaned so the hydrocarbon layer and waterline can be inspected properly.
Before cleaning, drain the unit and remove collected hydrocarbons into an approved container for proper disposal. Once the hydrocarbons have been removed, the chamber may be cleaned with mild dish soap and fresh water.
A small amount of hydrogen peroxide may also help break down organic buildup, depending on the condition.
For light cleaning between service intervals, a magnetic aquarium-style cleaning tool may be used on compatible clear viewing panels.
The goal is to keep the chamber clear enough for visual inspection, hydrocarbon monitoring, and proper separation performance.
Eco-Drain and Eco-Alarm
Eco-Drain separates hydrocarbons, but it does not notify the user when the chamber needs attention.
That is where the Eco-Alarm adds another layer of protection.
Eco-Alarm monitors hydrocarbon accumulation inside the Eco-Drain and alerts the captain, owner, or engineer when a rapid leak or buildup may require inspection. The user can then inspect the Eco-Drain, identify which Arid zone collected the contaminated fluid, and trace the issue back to the source.
In simple terms:
Eco-Drain separates. Eco-Alarm notifies.
Next Step
Eco-Drain is part of Arid’s eco-friendly product line and is designed for vessels that need an added hydrocarbon separation step before discharge.
If your boat has oily bilge conditions, diesel residue, hydraulic fluid exposure, or machinery spaces where contaminated bilge fluid may collect, Eco-Drain can help add a cleaner, more responsible discharge path to the Arid Bilge System.
The next step is choosing the correct Eco-Drain model for the vessel, the Arid system, and the discharge layout.
