We used the fresh water tank for the first time on our 2008 189FBS and the drain plug barely lets water out no matter what position I put the spout in. Is there a trick to it? I ended up opening both faucets and the gray water until it drained.
remove the valve you may have some plastic stuck in the opening. I removed mine and place a 1/2 ball valve there and ran it to the side of the steps with another 1/2 valve. I leave the one under the tank open and then use the one by the steps t drain, beat crawling under the trailer
I noticed that mine didn't drain well when there wasn't much water in it. It slows down a lot. I simply went about doing something else for a while. When it had lots of water, say 10 to 40 gallons, it was like the proverbial cow and the flat rock!