If you lay down a pipe along the factory with no space between pipe and factory then any automatically generated "bulk factory input/output" pipe will prevent the liquid from flowing past that one pipe.
Also if two factories A and B share a single pipe and you set A to output and B to input and place factory A before B, then B will not accept any liquid from the outside and only accept liquid from Factory A if the generated "bulk factory output" pipe on the outside is not connected with any other pipe which still accepts liquid.
