I got water in fuel one time. The water separator caught it in time. If you pull the tank drain plug (if you have one) you will have a mess, and the receptaple for the drain plug probably has a short sleeve protruding up inside the tank (for the drain plug to thread into) which will trap a good amount of the water inside the tank. Instead, tilt the RV so that the fill port side is lower. This will allow the water to collect on the lower side of the tank. Insert a curved 1/4' or 3/8" bendable copper tube thru the fuel fill port until it reaches the bottom of this low side in the tank. Connect a short piece of flexible hose to the end of the copper tube and start the siphoning process. Siphon out the water until fuel starts to come out. Any water left (in any) in the tank will be taken care of by the water separator filter.
Monaco Knight PDQ38,2007
RR8R Chassis, ISC330 Cummins