Backyard Aquaponics
A place to discuss aquaponics

I did manage to get the white hex screw thingy unscrewed on the bulkhead and now I need to see if I can make a bell siphon using the screw cap as part of the bell siphon. Any setups with the screw cap as the siphon? Any specifications on pvc parts?

it was discussed here..... with a pictures and other links.
viewtopic.php?f=1&t=26333

the other option is to keep the cap on and simply make a new hole for the siphon / standpipe.

either works.

note that the usual problem is actually getting snug fits as different brands are slightly different.
so there is no exact solution, sometimes you have to fiddle a bit.

problem for you is this thread discusses Australian products which are based on British Pipe Standard (BSP).
Not sure if your US sizes correspond. But it gives you the idea.

some of the posts and links give you alternate ideas on how to do it.

There was a threaded bung in the middle of my IBC cap

I releived around it on one side to get some extra space with a dremel - die grinder would do the same job

For the stanndpipe I used a slip fitting to male BSP fitting adaptor, the standpipe is just pushed in so that the bed can be drained, or the standpipe height changed.

On the underside I used the female version of the same fitting - the thread on the IBC was quite shallow so the female fitting just screwed onto what was protruding through. I added a bit of thread tape to keep things tight.

No photos as I didn't think anyone would find it "that" interesting

This is what my standpipe is jammed into: https://www.bunnings.com.au/holman-20mm-x-3-4-press-pvc-bsp-male-thread-adaptor_p3142740

I don't know how common BSP is over there. In most cases, especially in soft fittings (copper, plastic), you can get away with using NPT and BSP together, but I wouldn't be using them under a lot of pressure.

The key thing is to make sure that the threads per inch are the same/very close. You can see in the chart on this site that in 3/4" you'll have no issues, up to 2" they're close enough, but after 2-1/2" you're going to have some serious problems!

http://pipeandhose.com/?q=node%2F2

having a bit of plumbers tape handy doesn't go astray....helps make the thread and fits just that little bit tighter when required.