Installing a bilge pump requires some mechanical and electrical ability and a lot of common sense. The best set up requires 2 pumps one high capacity pump big enough to deal with a catastrophic emergency will do a poor job of keeping the bilge dry because the water in the discharge hose can drain back into the bilge when the pump shuts off and a big pump requires a big hose. The ideal bilge pump arrangement is a small, 500 gph, automatic pump mounted in the sump to remove rain and shaft-gland leakage, combined with a high-capacity pump, 4000 gph, unit mounted higher to deal with more serious flooding. Using a 1/2-inch discharge hose on the small pump minimizes the backflow from the hose when the pump cycles, thereby maintaining a dryer bilge. A simple, and effective, way to prevent back flow is to install a ball, or flapper, check valve. The large pump should be wired to a water switch, or a manual switch might make more sense, it depends on your circumstances and preference. An added advantage of this set up is that the high-capacity pump sits high and dry meaning little or no use giving it a long life expectancy.
The pumps must be solidly anchored to either the hull or a bulkhead. Boats rock and pitch and an unrestrained pump will go out of position with the possibility that the pick-up, or suction, will end up out of the water and the pump will be of no use. The other issue is that the high capacity pump will be heavy and , like a bowling ball, will knock around all over the place in the bilge and possibly cause damage.. Drilling holes in the hull is, obviously, not a good way to anchor the pump. A better way is to make a base out of 2 x 6” treated lumber, attach the mounting studs to it, and then use epoxy to secure it to the hull or bulkhead. For the same reasons float switches must also be secured.
The last thing you want is any restriction in the discharge hose, therefore, only use smooth hose, tubing, or pipe and any bends should have the largest workable radius. You also need to keep the hose runs as short as possible. Remember, bilge pumps are the same as sump pumps and are high-volume, low-pressure affairs. The hose / tubing should also be flexible so that it can flex with the pitching and yawing of the boat. You will also want to connect the hoses to their respective fittings with good quality, stainless steel hose clamps with 2 clamps, opposed, at each connection. Clamps are made by several brands such as Ticon, Ees Teck, and Lokman however, one of the very best is Tech Team’s #727 https://techteamproducts.com/product/3-inch-hose-clamp-set-8-pieces/ https://www.amazon.com/dp/B07GZZ1KHV?ref=myi_title_dp these clamps have stainless steel bands, housings, and screws. For other options you can do a hey Alexa or hey Siri search on Google, or watch the you tube video https://youtu.be/q5IiwTPVIdo
You also want to install the discharge port well above the water line and above the sharpest angle of heel for 2 reasons. First, surging water can reenter the system, flood the bilge and cause the pump to short cycle and second , since the hose is full of water, it can create a siphon with the same result. Once again, a check valve will mitigate this problem.
Both pumps will be fed with waterproof wiring and connections with standard UL 3 prong plugs therefore, you will need a fused outlet above and well out of the bilge area and when you install the pumps, make sure the wires to the pumps are strung out of the water and supported with cable ties every 12 – 18 inches. Since the high-capacity pump draws a large amount of current, it would be a good idea to have separate outlets for each pump and they should be independently fused with circuit breakers.