I did not see this made clear in the ISAF rules being cited, but the 'unspoken' rule is that NO bilge pump expected to be used for emergencies (and what other kind is there?) should ever share a through-hull with any other fixture or drain. Every bilge pump should have its own dedicated through-hull, switch, fuse, seacock, handle, and so on. If you happened to have three pumps the idea would be that all three could be operated independently or together, at the same time, with no interference.
I would NEVER rely on a bilge pump that had to drain into a cockpit and thus rely on the cockpit drains. What if the cockpit drain were the source of water coming into the boat? --and this is probably very likely. Ditto for an on-deck discharge that relied on deck scuppers.
Having a side-located through-hull for a bilge pump becomes a problem when the boat is heeled. This is why ISAF suggests a cockpit drain aft. If there is no vented loop in the discharge line, the discharge through-hull will suck rather than drain. One should make every effort to drain the pumps as far aft (and parallel with the centerline) as possible.
Especially for a very long (hopefully straight) discharge run, you can fit a check valve in the line, at the highest rise which should be immediately after the pump, to avoid the hose-full of discharge line draining back into the bilge when the pump shuts off, thus activating the float switch again and kicking the pump back on over and over till you become annoyed and turn it to 'off' or the pump burns out and/or battery dies. There should be no unnecessary dips, corners, or rises in the discharge line. Try to make the run beyond the highest loop drain downwards on its way out so at least out of the water the hose will be empty. I would NOT recommend PVC pipe for this, only the rugged Shields 148 holding-tank hose (or its Trident equivalent).
There are plenty of 'creative' ways to dewater a boat. These have been used throughout the ages. One is a Y-valve on the engine intake that allows it to suck water from the bilge, not the sea. This is for emergencies only, obviously. The nightmare I heard of was a boat striking something-- it went down in about 2 minutes. Someone on board had the presence of mind to start the engine, which probably added a minute to the abandon-ship time. The boat went down with the engine running... but that engine saved lives.
You can do the same thing with a deck-washdown pump.
Another idea is to have a large (2"?) drain plug towards the bottom of a gray-water or holding tank. Pull the plug, let the tank flood, and use the pumpout pump to assist the bilge pump.
You can do the same thing in an emergency by discharging a hand pump into the sink.
Every electric-only pump should have a manual backup. To my mind (and in my boat) the Whale ones are the best manual pumps in the world (Royal Navy spec). The double-diaphragm design ensures at least half the power even if one side breaks. Some of them are almost as efficient as an electric one.
In going to sea (and for the same reasons when leaving a boat for long periods at a dock) a backup electric pump is key. At CY we conceived of the 'bilge pump on a stick' --not a robotic delicacy but the pump and float switch mounted on a long plank and lowered vertically into the depths of the bilge so as to be easily accessible-- just unbolt the top end of the stick and withdraw the whole arrangement. The C44s get TWO bilge pumps on a stick, one about 6" higher than the other. A red light on the panel comes on when the second one kicks on, indicating that the first one failed and there is 6" more water than usual in the sump. Then when you carry a spare, you've got it covered. Those Rule pumps are actually very cheap-- too cheap to rely on 100% and too cheap to not carry spares to sea.
The last Cherubini 44 we built had 7 different, simultaneous ways to dewater the bilge-- and this on a hull that is renowned for NOT leaking (only a seacock failure or hose failure can admit water below the waterline; the boat is too rugged to crack and has no keelbolts to leak). Dewatering is not an issue to take lightly because you will only find out the true inadequacy of your pumping situation when you would really like to find it works above expectations... and if it does not, it's too late for it to matter.