Plumbing Newbie

[Cliff]

You could do a type of duriso standpipe with that set-up. The part with the air hole would have to be higher than the tank to prevent water from coming out of it

[Mandosh]

Your going to want to replace that 90 with a T. Put a cap in the top of the T with an air hole drilled. I you want to get fancy you can run a piece of air line with a valve out of the air hole.

What your going to have to make is an external durso standpipe. If you google it you should be able to find diagrams.