Bulkhead fitting

[Jasongtr]

Just about to start plumbing my new tank, it has 4x bulkheads in a central weir section through the bottom glass.

my LFS who have been great so far have told me to put the rubber seal on the outside as they said it doesn’t matter whether that’s inside or outside and the use aquarium safe silicone sealant on the inside, the bulkhead has two large nuts and one rubber sealing washer.

How does that sound? Obviously I’ll only be wanting to do this job once

thanks

 

[TheBear78]

Rubber inside where the flange and coupling are one piece. The loose nut goes outside for applying light pressure to the rubber seal.
If you put the rubber on the outside with the loose nut inside you'll have fun tightening it and the water pressure can push past any gaps on the outside.
If you put the loose nut outside with the rubber seal nothing is sealing the thread.
Silicone will help but its not supposed to provide the seal.

 

[Jasongtr]

Rubber inside where the flange and coupling are one piece. The loose nut goes outside for applying light pressure to the rubber seal.
If you put the rubber on the outside with the loose nut inside you'll have fun tightening it and the water pressure can push past any gaps on the outside.
If you put the loose nut outside with the rubber seal nothing is sealing the thread.
Silicone will help but its not supposed to provide the seal.

My bulk head has two nuts and one rubber seal washer, the white part is a threaded part to fit the pipes to inside the weir

 

[TheBear78]

OK, I assumed you had one which is like a nut and bolt.
If you've got a threaded tube and two seperate nuts then I personally wouldn't use that. Silicone doesn't stick to plastic very well so I would be worried about leaks.
I've always used this type:

 

[TheBear78]

I see you added a photo. Assuming that the white coupler is half threaded and half plain it can only really go one way with the parts that you have.
Do both nuts turn?

 

[Jasongtr]

I see you added a photo. Assuming that the white coupler is half threaded and half plain it can only really go one way with the parts that you have.
Do both nuts turn?

Yes the threaded coupler has a thread one end that screws into the bulkhead and both nuts turn on the bulkhead