plumbing trapezoid overflow with back

[andrewkw]

I forget how to do this and rather than spill or incorrectly glue I'll ask instead of making a mistake then coming back and asking...

I have a 3 sided trapezoid overflow so it has a back with a hole in it and is held to the side of the tank with a bulkhead and not held with silicone. Do I use one gasket between the inside of the tank wall and the outside of the overflow box or 2 gaskets, one there and one between the flange of the bulkhead and the inside of the overflow box as well. Or reverse the bulkhead? This would mean the gasket would be on the outside of the tank which usually is a no no. I found some old threads with some pretty reputable posters suggesting reversing the bulkhead but concern will be tightening the bulkhead backward will be very difficult and I don't want to risk hitting the eurobracing with wrench.

If I was going to make this tank a new reef I'd probably scrap this old overflow box and go with a much lower profile one but this is a simple fish only and I have all these parts on hand. I even managed to find an extra gasket should I need to use 2 although that one is old (the bulkhead is new of course).

thanks in advance.

 

[BlueRoofTang]

On a bulkhead, you use one gasket, on the inside, which is the flange side...NOT the nut side.

 

[Gorgok]

If the box is being held by the bulkhead you can: put the bulkhead flange, gasket, box, gasket, tank, then nut; or nut, box, tank, gasket, bulkhead flange.

The goal being to make a continuous seal from the tank to the bulkhead flange. If you skip the second gasket on the first example you will have a weeping path between the box and the tank and out the threads. Inside or out doesn't matter as long as its sealed from glass to flange.

 

[andrewkw]

If the box is being held by the bulkhead you can: put the bulkhead flange, gasket, box, gasket, tank, then nut; or nut, box, tank, gasket, bulkhead flange.

The goal being to make a continuous seal from the tank to the bulkhead flange. If you skip the second gasket on the first example you will have a weeping path between the box and the tank and out the threads. Inside or out doesn't matter as long as its sealed from glass to flange.

Thanks. Initially I tried the single gasket against the inside of the tank and outside of overflow and still had a slow drip. Luckily I did have the second gasket and put that inside the overflow box against the flange and everything is good to go for gluing.