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If it still works, it will open before the pool is completely empty. But are you sure the valve is hydrostatic?

If it is not, then you will need to shop-vac the water remaining over the bottom drain, remove the drain cover, shop-vac the water under the cover, and then remove the lug nut and slide out the (manual) relief valve.

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2010-06-22 17:17:12
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Q: Will the hydra-static valve in main drain open if you empty the pool?
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