leaking from bulkhead?!?!

[reefwars]

Orca can be used under water

[GoFish]

It looks like you have a nut on the topside (underwater). A nut on the bottomside and also your barbed fitting is threaded into the pipe coming down? Is that correct?
You could try using a pipe wrench on the top (not a dirty old shop one) , as long as the bulkhead has a rubber gasket and not silicone (as that would probably make it worse). The bottom nut looks like it could only be tightened using some McGuyver skills (a custom tool that would look like an angle grinder wrench with long posts). If its leaking from where the 'barbed' fitting that screws in then you could use a balloon or condom and a tight rubber band to stop the flow while you spun that out and Teflon taped or siliconed that connection?

Originally Posted by reefwars

Orca can be used under water

This may be your best option if used from the topside

It doesn't look like the right type of fitting to use to begin with?!