Industrial scale pumps certainly exist, but they aren't exactly small and easily portable. I'm not familiar with the one Holland sent England, but I suspect it

Industrial scale pumps certainly exist, but they aren't exactly small and easily portable. I'm not familiar with the one Holland sent England, but I suspect it was pre-assembled on a ship? The highest capacity pumps in New Orleans can move roughly 10,000 gallons a second, but they require a supply "hose" that's ~8-10 feet in diameter to reach that volume. You'd need to get an enormous hose to a low point of the cave system, which may not be near the entrance. Then there's the question of what to do with the water you pump out. Maybe there's a river nearby that can absorb it? It is doable, but it's neither simple, not particularly quick.