While the pool is filling it is a good time to get the equipment ready for operation. Normally when a pool is shut down the drain plugs are removed and then stored or put back in place, I generally try to place the drain plugs in the pump skimmer. Each piece of equipment usually has a drain plug of some kind. Most pool pumps have two, one in the front of the pump pot and one in the back section section before the motor. The plugs will be toward the bottom of the pump. The filter plug should be in the bottom of the filter, you may need to look in the back. Heaters have a plug and most other equipment. I recommend inspecting all the plug o-rings for cracking, if they look good cover them with a thin layer of a Teflon based lubricant  to get them viable again before putting them back in.  Using Vaseline or a petroleum based product can damage the material of the o-ring and cause premature failure.

I wish you a happy pool season!