I'm sorry to have to tell you this - but InfoPath offers no way to do this unless you write custom code, or use an add-in like qRules.
Unless your form is a database bound form? That is, you created the form off the database? But otherwise, the user has to manually insert the rows. If you know the maximum number of tanks you may have, you could by default include the max, then hide any you didn't need.... but you wouldn't be able to set the values for the tank based off the selected warehouse - a rule on the field where the warehouse is selected would end up setting all instances to the same value (again, something that qRules can help with, or you would be able to do with custom code).