A bilge pump is easily considered one of the most important components to the life of your boat. It works by sucking up all of the unwanted water that collects at the bottom of the boat and pushes it back out into the lake or ocean via a hose. It also serves as a great filter to keep all of the oil and debris that can live in a lake (or the ocean) away from all of the important working mechanisms of your engine. As a general rule of thumb, an eighteen-foot boat would do well with a 500 GPH bilge pump, a twenty-eight-foot boat with a 1,000 GPH bilge, and a forty-five-foot boat with a 2,000-4,000 GPH output. If you want to see how a bilge pump works right in front of you, you can fill a bucket with five gallons of water and see how long the pump takes the remove this water. A 500 GPH pump should be able to complete the task in about thirty-five seconds, while a 1,500 GPH pump will be able to do the same in about twelve seconds.