We have 4-7 velcro flap water drains to drain our wet inflatables efficiently, big wet inflatables have more drains(for example, inflatable water slide with slip lanes). We got 2-4 rain drains on the main body, 2 in the slip lanes and 1-2 pool drains. Waterproof tarp on the slide is hot welded seam and keep more than 90% water from getting inside.