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Sump pumps can be rented for about $36/24 hours. Do this early in the day so your pool is empty before dark. Your rental should include rubber fire hoses in 50 feet (15.2 m) lengths. Two should be enough for most homeowner, but check to make sure the pool is not more than 100 feet (30.5 m) from your clean out/sewer access point. This step is very important. Most municipalities won't let you drain your water directly into the street or a neighbor's yard, for example. That leaves you two options of where to drain the water:  Directly into the clean out. This is usually a 3 to 4 inch (7.6 to 10.2 cm) plastic pipe on your property, usually outside a bathroom or the kitchen, with a screw cap on it which leads directly into the sewer. The city will reuse this water. On older homes, one clean out usually exists and is elevated on a wall. On newer homes, two clean outs usually exist, and they are ground-level — sometimes obscured by landscaping. Using a clean connected to a wall is risky and could cause water damage to the house. If your clean out is connected directly to your house. Consult a pool specialist or general contractor before proceeding.  Irrigate the lawn, plants, or other shrubbery. This is not recommended if you are draining the entire pool, nor is it a great idea on certain lawns or plants that don't react well to excessive salt or chlorine. Certain grasses and Oleander species can take pool water, but citrus, hibiscus, or other salt-sensitive plants should not be irrigated in this fashion. Make sure the hose is properly attached and make sure the other end of the hose is stuck into the clean out before plugging in the pump. Some hoses will go down about 3 feet (0.9 m) into the clean out before hitting something; make sure to lodge it in properly. The time it takes to drain your pool water will depend on the municipality laws, the pump speed, and the total size of the pool.  Although it may sound strange, check your municipality's laws concerning the discharge rate. In some municipalities, the discharge rate is capped quite low — Phoenix, for example, sets theirs at 12 gallons (45.4 L) per minute (or 720 gal/hr). This ensures safe disposal of the water into the sewer. Most good pumps will far exceed the municipality's maximum discharge rate. They'll function safely at 50 gallons/minute, and top out at about 70 gallons/minute. Your pool size will also determine how long it takes. If you're pumping at 30 gallons/minute, or 1,800 gallons/hour, and you have a 25,000 gallon (94,635.3 L) pool, it will take roughly 14 hours to drain the pool. Do this especially if your water is dirty, as this will save you time in the end. Try some brushing while you are at it. How much water the pump is able to remove will depending on your pool's contours at the deep end.  Drain the last foot or so manually with two buckets. This is where a helper comes in handy.
Go to a home improvement store and rent a submersible sump pump. Set up the sump pump and discharge hoses, connecting the hoses to a clean out. Lower the pump into the pool and plug it in. Watch your water disappear, monitoring the discharge carefully. Every foot or so of water level decrease, spray the perimeter of the pool's previous water line with a hose. Wait as the pump removes almost all of the water, draining the last bit manually.