LiquidHopper
I've implemented the LiquidHopper as mentioned in https://github.com/BuildCraft/BuildCraft/issues/1291 and https://github.com/BuildCraft/BuildCraft/pull/1310 in the BuildCraft repo. It seems like the main BuildCraft devs didn't like it after all, so if you want you're welcome to add it to ADO.
The code for it can be found in my fork of BuildCraft: https://github.com/rubensworks/BuildCraft/commit/80ab099b9bcf04d9213e1e5ae7184564a82412a7
I don't know if you would need anything else?
Sounds good to add, I will do it in a few days. Too much work this week :/
It's not that they didn't necessarily like it. You just have to discuss changes in mechanics with the devs first BEFORE submitting a PR.
Well, the feature request issue was open for quite a while. I also couldn't find any information on how to directly contact the main devs.
IRC, #buildcraft, irc.esper.net. Learn to IRC :)