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Grommets are used to create watertight seals for the plumbing of hydroponic systems such as NFT systems, DWC systems, Dutch Bucket systems, water reservoirs etc.

A hole is drilled and the Grommet is inserted into the hole. Piping is then pushed through the grommet which will form a watertight seal.

Irrigation Piping, Ring Grommet and Top Hat Grommet measurements (approximate, in mm) follow below:

Product – General NameOuter DiameterInner Diameter
5mm Irrigation Piping64
6mm Autopot Piping6.34.2
9mm Autopot Piping96.5
16mm Autopot Piping18.512.5
12mm Irrigation Piping1612
15mm Irrigation Piping1815
20mm Irrigation Piping2421
6mm Grommet for Reservoir105.5
12mm Ring Grommet1912
15mm Ring Grommet2015.5
20mm Ring Grommet2318
25mm Ring Grommet3225
6mm Top Hat Grommet106
9mm Top Hat Grommet13.59
16mm Top Hat Grommet1915
19mm Top Hat Grommet2318

Based on the above the following grommet & piping combinations are advised:

9mm Autopot Piping (for use with Autopot Aquavalve 5): 9mm Top Hat Grommet

5mm irrigation piping: 6mm Ring Grommet or 6mm Top Hat Grommet

12mm irrigation piping: 16mm Top Hat Grommet works beautifully. 12mm Ring Grommet fit will be a very tight fit, while a 15mm Ring Grommet’s fit could be a little loose (This could be countered by using an insert fitting (eg. straight connector/T-piece/elbow) inside the piping at the point where it goes through the grommet, to flare out the piping and create the waterproof seal)

15mm irrigation piping: 19mm Top Hat Grommet, or 20mm Ring Grommet

20mm irrigation piping: –

25mm white PVC electrical conduit: 25mm Ring Grommet


Hole Saw Sizes for Grommets – Please note: these hole saw sizes are for flat surfaces, not for curved surfaces. A slightly smaller hole can be tried on curved surfaces to prevent possible leakage due to the curving of the grommet on the curved surface. (Drilling test holes and testing if seals are watertight is always advised)

6mm Ring Grommet: 9mm drill bit

12mm Ring Grommet: 19 mm Hole Saw

15mm  Ring Grommet: 19mm Hole Saw

20mm  Ring Grommet: 25mm Hole Saw

25mm  Ring Grommet: 31mm Hole Saw


6mm Top Hat Grommet: 9.5mm drill bit

9mm Top Hat Grommet: 12.5mm drill bit

16mm  Top Hat Grommet: 19mm Hole Saw

19mm  Top Hat Grommet: 21mm Hole Saw


It is not recommended that Petroleum Jelly is used as a lubricant. A silicon lubricant, although more expensive, is better. Olive oil can also be used. Throwing grommets into HOT water before installing also helps a lot.

Please note if grommet is fitted and then taken out a number of times, it may stretch and warp.

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