Black rubber bulkhead fitting, 25 mm, for a 3 mm wall thickness.

48 mm bulkhead seal with narrow groove for a 2 mm wall

48 mm wide-groove tank grommet for 5 mm wall thickness

Black cap seal seen from above, with its 6 mm central bore

Flat white EPDM washer, 24 mm, seen from the front, with its 15 mm central bore

White EPDM flat washer laid at an angle, showing its low thickness

Bulkhead fitting and flat washer 3/4, from 6 to 48 mm

Name: Bulkhead fitting and flat washer 3/4, from 6 to 48 mm
Brand: Terra Aquatica
SKU: TA-PASSEPAROI-13-5
Availability: InStock

$2.00

$0.66 × 3 with no fees Klarna.

These rubber bulkhead seals, also known as grommets, provide a watertight seal where a pipe passes through the wall of a tank or container. They are available in 13, 25, and 48 mm for walls of 2 to 5 mm, with a reducer from 25 to 12.5 mm and a small cap seal that seals the passage of a 6 mm diffuser. The flat EPDM washer, sold in packs of 10 or 25, seals a threaded 3/4-inch fitting.

Ref. TA-PASSEPAROI-13-5·Seal

Model : Bulkhead fitting 13 mm, wall thickness 5 mm

Bulkhead fitting 13 mm, wall thickness 5 mm

Bulkhead fitting 25 mm, wall thickness 3 mm

Reducer 25 to 12.5 mm

Bulkhead fitting 48 mm, wall thickness 2 mm

Bulkhead fitting 48 mm, wall thickness 5 mm

Cap seal, 6 mm bore

EPDM flat washer 3/4, pack of 10

EPDM flat washer 3/4, pack of 25

Customer support 7 days a week by email

Delivery within 2 to 15 business days

100 % secure payment

The summary

What you receive: a seal of the chosen model — bulkhead fitting for 13, 25 or 48 mm, reducer from 25 to 12.5 mm or cap seal for 6 mm, or a pack of 10 or 25 flat 3/4 seals.
The choice: made according to the pipe diameter and the thickness of the wall to be passed through.
The hole size: 39 mm for the 25 mm bulkhead fitting; for the others, drill to the diameter of the base of their groove.
Fitting: by hand, with the seal wetted, no nut or adhesive required.

Bulkhead fittings for passing a pipe through a reservoir wall, with no nut or adhesive required

Passing a tube through the wall of a bucket or reservoir without leaks normally requires a bulkhead fitting with a lock nut, rigid and cumbersome. A through-wall grommet does the same job with a single flexible part. It sits in a hole drilled in the wall, held by a groove that grips the edge of the hole, and the tube is then pushed through the centre, compressing the seal against the wall. The result is a watertight pass-through, removable by hand.

13 mm, 5 mm wall

Wide rubber collar, for a 13 mm tube.

25 mm, 3 mm wall thickness

39 mm hole, pipe with a 25 mm outer diameter.

Reduction 25 to 12,5 mm

Fits into the 25 mm seal for a 12.5 mm tube.

48 mm, 2 mm wall thickness

Narrow rubber grommet, for a thin wall.

48 mm, 5 mm wall thickness

Wide groove, in thermoplastic elastomer, for a thick-walled fitting.

Cap seal, 6 mm

It seals the fitting where a diffuser passes through its line.

📏 Choosing the right model

Two measurements determine the model. The first is the outer diameter of the tube that needs to pass through: 13 mm, 25 mm, or approximately 48 mm. The second is the wall thickness, as the seal groove must match that thickness in order to grip the edge of the hole without any play. A groove that is too wide lets the seal float and leak; one that is too narrow prevents it from seating properly. You therefore measure the wall with a calliper before choosing between the narrow 2 mm groove and the wide 5 mm groove.

Fitting a water-level indicator on a pot

In the hydroponic pot with reservoir, the 25 mm seal and its reducer hold the level tube that indicates the solution height. The same assembly can be fitted to a bucket or tank of your choice to add a transparent level indicator, visible without lifting the lid.

Drilling to the right diameter, burr-free

A hole that is too large will not grip the seal properly; a chipped edge will cut through it and cause a slow leak. Drill with a hole saw, 39 mm for a 25 mm seal, or at the groove-root diameter measured with a vernier calliper for other seals, through a flat surface, then deburr the edge with a craft knife. Run a clear-water test overnight before filling with nutrient solution.

Assembly is done by hand. Wet the seal with water or a water-based lubricant, pinch it to push it into the hole, then check that the groove sits flush all the way around the edge. The tube is then pushed into the centre with a twisting motion, which compresses the rubber against the wall. For a 12.5 mm tube, first insert the reducer into the 25 mm seal, then the tube into the reducer.

Take a 20-litre bucket whose level you want to monitor. Drill a 39 mm hole 3 cm from the base, fit the 25 mm seal followed by the reducer, and push in an elbow connected to a 12.5 mm transparent tube, running vertically up the side of the bucket. The solution level is then visible at any time.

🧪 Rubber and elastomer

The 25 mm seals, the reducer, and the 48 mm narrow-groove seal are made of black rubber; the 48 mm wide-groove seal is made of thermoplastic elastomer. The 13 mm seal is also black rubber, and the cap seal is black elastomer. Both materials remain flexible in water and withstand standard nutrient solutions. Check them each time you clean the reservoir, and replace them as soon as they harden or crack, which tends to happen most when exposed to light.

💧 The 3/4 flat washer

Whereas a bulkhead fitting passes through a wall, the flat EPDM washer seals a threaded fitting. It sits between a 3/4-inch plug or fitting and the surface against which that fitting is tightened: compressed by the tightening, it fills any irregularities in the seating and stops water ingress. Its 34 mm outer diameter and 15 mm bore match this thread size. In the hydroponic guttering system, it is fitted to the plugs that seal the gutter ends, and the 20-plant model uses 8 of them. EPDM is a synthetic rubber that remains flexible under permanent water contact, so the plug is tightened by hand, without tools. The pack of 10 covers one full drain-down of a 20-plant system, with 2 washers to spare.

🔧 Replacing a worn seal

A weeping seal takes just a few minutes to replace. Drain the tank below the level of the hole, remove the tube and then the seal, clean the edge of the hole, and fit the new seal wet. To chain several pots fitted with these through-fittings, the dual-channel branch tee carries both the supply and return of the solution through a single fitting, and the hydroponic system maintenance guide covers leak checks.

Technical specifications

25 mm bulkhead fitting

Wall: 3 mm
Drilling: 39 mm
Material: Rubber, black
Reduction: Towards 12.5 mmSold separately, with this gasket only

Other seals

48 mm, narrow groove: Wall of 2 mmRubber, black
48 mm, wide groove: Wall of 5 mmThermoplastic elastomer
13 mm, wide groove: Wall of 5 mmBlack rubber, 26 mm collar, 14 mm height
Cap seal: 6 mm boreBlack elastomer, 12 mm high, for a diffuser on its irrigation line
Joint plat 3/4: 24 x 15 mmOuter and inner diameters, for a 3/4-inch thread
Flat gasket, material: EPDM blancHand-tightened under a gutter end cap

Manufacturing

13, 25 and 48 mm narrow, reducer: India
48 mm wide-bore: Belgique
Cap seal: Belgique
EPDM flat gasket 3/4: France

To budget for separately

Drilling: Hole saw 39 mmFor the 25 mm washer
Pipe: Rigid tube from 12.5 to 25 mm outer diameter

8 further specifications are available in the detailed view.

In the box

1 seal for the chosen model, or 10 or 25 flat seals depending on the batch

Diameters, wall thicknesses, drillings, materials and origins checked on 02/10/2026 and 07/10/2026 against the component technical datasheets, the manufacturer's 2026 price list and the guttering system parts list.

Estimate your
delivery time

Seal dispatched by tracked parcel from France. Exact shipping costs and final delivery times are displayed at checkout once your address has been entered. Outside the European Union, import duties and taxes are the responsibility of the recipient.

Frequently asked questions

6 questions

6 key questions

What diameter to drill?

Is the reducer used on its own?

How do you lay it without tearing it?

Do you need to add silicone?

Narrow groove or wide groove?

Can it withstand the pressure of a pump?

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Bulkhead fitting and flat washer 3/4, from 6 to 48 mm

The summary