300 gallon tank

Hi, I'm currently a college student and at my college we have a 300 gallon tank. For the last two years we have been trying to set it up. Due to busy schedule of students and now covid, it has remained almost empty. My professor is dead set that we use our Reverse Osmosis machine to fill the tank, but this takes forever to pump out all the water, it only holds 12 gallons, and takes a day to refill. Can I use tap water and just use water conditioner? How can I fill this tank faster as I would like to get it cycling and get live rock in there by April.