When starting to vacuum, put the bottom of the vacuum up to the return to fill the hose, with the vacuum cap in the skimmer. As soon as the air bubbles stop and water runs out, put the cap on the skimmer to start to vacuum. When finished, lift of the vacuum head to let air in and suck all water out, holding on to the cap - as soon as you can feel the cap move, remove it - you will have hardly any water left in the hose

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When the water in your pool is not up to the skimmer yet, and you want the pump on filter, you can use the vacuum head and pole to use the water from the pool to go into the skimmer. You can also drain your pool this way too 8)
When testing your pool water take the sample from the place that gets the least circulation - like near the ladder, this way you be sure that all the water in the pool has the right amount of chemicals. Get your sample from about 8" down.
Here is my favorite - if you need to clean the scum line - get in and enjoy the water while you do it :-D