If you got water in the tank, and didn't drain the tank FULLY, there will still be water there. Water sinks to the bottom of the tank, and won't mix with the gasoline. If your pump pickup is where it should be...you might be drawing water as well as gas into the pump. As a young guy, I worked at a bunch of gas stations and when we had to check the water level of the inground tanks, we'd smear some marking gunk on the end of the long stick we used, and submerge it into the tank. When it touched water, it turned from green to red, so we could tell how much water was there.
HEET (alcohol) will eventually separate from the water too, so it probably didn't work well enough as a 'drying' agent.