They mean not to connect to thruhulls below the waterline. If you are connecting a bilge pump
to a thruhull above the waterline, then this is OK.
However, that stuff is very thin and cheaply made. It is easy to break or get holes in it and it kinks easily. And the corrugation cuts the flow down by a lot - severely de-rating your bilge pump
You can't use vinyl hose or the exterior-ribbed vinyl hose? This stuff is much better and can be bent into small radiuses without kinking.