Hello EpicSlayer7666,
So the long and short of it, is that is how the mod is designed and works. Its the only way to be able to track which offshore pumps are active. The Devs in there infinite wisdom decided that Offshore Pumps are Always ON, Always Working and flow rate goes to 0 when then connecting entities fluidbox equals 100%. Essentially meaning I have no way to ask, is it on, is it active or is it pumping? I've have to use the fluid statistics and a ton of calculations and logic checks to even get the mod working.
So the mod presumes that if you connect anything to a pump, that it is active and pumping, providing some fluid for the fluid statistics. The mods logic and math works out which areas and how many pumps, to its assigns the correct % to each area. But the Mod is making a best guess, as you say if you don't connect anything up afterwards, you are throwing away water.
I've asked and been ignored by the devs in trying to get offshore pumps changed to provide me with something to use, so the only other way to do this, would be to code a new entity from scratch where i can make my own statuses and readings. This is not something trivial and beyond the work of the mod at the moment. It would be one of the final long standing goals, but would require significant work to do and is something I don't have the time to do.
When you play with this mod, just come with the understanding that, if you put a pipe connection onto the pump, the mod considers it active, if you don't want that or are not ready, then leave that pipe/storage-tank/pump until the last one to connect.
As for your second point, the calculations and maths should be ok, but I may just need to check what pumps fluidbox buffer is as I may need to write in some code for that. Pipes and Storage-Tanks are calculated from a Vanilla perspective.