Issue

Fluid pipes cannot connect to and extract from vanilla cauldrons. This makes lava farms harder to make.

Versions:

IC2C 1.19.2 2.0.1
Forge 43.1.47

Cauldrens arent fluid containers in code.
not a bug.

If you want a good relyable lava source, "Fusion Reactor" is your target.
It will be able to produce as much as you need.
Otherwise pump a lava cave lake or nether?