Maybe it's not the worst idea to interact with any external entities with fluid boxes? Either pipes or tanks. So you can support any fluid handlers. One storage tank can be used for 3 connections at a time because of its size (3x3).

Vanilla storage tanks are already supported with fluid connections, but they will only connect to factory buildings where they would connect to other pipes. This is intentional. Note that I'd like to support all kinds of pipes and tanks, not just vanilla ones, and it's almost possible, but right now the API doesn't support reading the capacity of an entity's fluid box, so I have to use a table of hardcoded capacities in the mod's code, and this table currently only contains vanilla pipes/tanks and bulk transfer pipes. I've already asked for an API extension, it should arrive with 0.15.