At present, the only way to store fluids outside of machines is long networks of large pipes.
As for automatic water collection, a Drain (cover) can be used to automatically suck up water immediately in front of it (if you have Finite Water off), or it can be placed on the top of a pipe or machine, and it will collect water during rain.
Thank you for your rapid answer !
I try the drain cover, but it seems like it didn't connect to any GT fluid pipe, neither to the small coal boiler... I don't know if it's a feature, or a bug ?