Dumb question, but how much of the plumbing do I glue in a drilled tank?

http://www.3reef.com/forums/new-hobby/bulkhead-installation-tips-111422.html

My Bulkhead Installation Tips sticky post should help answer some of your questions. You want to be able to remove your standpipes for cleaning and service or to adjust the height so I would never glue them to a bulkhead. You will find in the sticky, I much prefer thread x thread bulkheads for many reasons and this is one of them. I glue my standpipe to a slip x male adapter and screw it into the bulkhead by hand so it can be unscrewed easily in the future. Same with anything outside the tank too, I always use threaded fittings with a little LaCo PVC thread sealant on them so they can be removed or altered in the future rather than cuttting the bulkhead apart and tossing it.

 

^^ THIS +1.. I had a Chromi that ended up in mine every morning. I was starting to thing he was addicted to the ride down to my sump when I "flushed" him! All my stuff is dry fitted and still hard to take apart. No leaks at all

 

When the tank is finished and running:
If the outside of the pipe and/or fitting is dry, glue it.
If the outside of the pipe and/or fitting is wet, don't glue it.

That's about as simple as it is. Nothing better than being able to remove a pipe to clean or get a fish out.