if that ever happened to me, Id pay my lfs to use their change/service truck and bring me a 100% mixed up ready full water change. maybe enough for 2x 90% changes all at once so your fish can swim low and be in-tank during the drain. they can heat it and get the salinity ready remotely then truck it to me. Id siphon it all out the window, then they'd pump it back in from the truck. large tank cpr. they have a van with a huge storage vat in it for multiple changes around town as they do their circuit for maintenance at dr's, banks etc.