Current FluidContainerRegistry, does not allow for a dynamic fluid list to be generated without some issues to the meta list to occur. FluidContainerRegistry only allows for id and meta, NBT is needed for smooth addition/removal of fluids to the list.

IFluidContainers allow for a bucket, can, what have you to be filled with anything if done appropriately.

However, buildcraft doesnt seem to utilize the IFluidContainer at all for things such as filling a tank, choosing a refinery filter, etc.

Realistically only inventories should consider the IFluidContainers, as for basic tanks, the RClicking can be done on my side

I don't even know what you are asking, but I think its a duplicate of #1157

And since Forge still hasn't implemented a unified container bridge utility class (I even submitted one), the requirements for further development have not been met.
MinecraftForge/MinecraftForge#813

Well for the refinery, choosing the filter fluid is done through Containers; however, IFluidcontainers are neither drained nor filled in this instance, a getFluid would suffice.

Make a PR (one that isn't broken this time -.-)

Nah I'm good. I already did that once before, was criticized all the way through. You can do it. 😏
Also, that utility class isn't being accepted as the Fluid API is getting another rewrite iirc.

Ok, closing then. Since I still have no idea what you want.