I think it would be really useful, if you could read the amount of fluid that is in an iron tank. Using a comparator (similar how it works with vanilla chests) seems like an ideal solution.

I already created the pull request #360 that does this, but need some help/ideas on how to fix a bug with missing block updates (more detail on this in the pr). I guess I should have created this issue first... Oh well, if this turns out to be a bad idea and my code is not accepted, then I just have to live with it.

@Yopu thanks for your help on this issue. Only one small thing left. If you have a setup like the comparator doesn't update it's value unless it gets a blockupdate. With a vanilla chest this works just fine. So to be consistent with vanilla behavior we should also make setups like that work.

And yes, there is a valve behind the top cobblestone.

Investigating.

Fixed: dca915b

Thanks for the heads up @wshadow!