I have installed a bilge pump in my 24' kevlar double and another in my 19' carbon single. In the double, I installed it behind the rear seat (there was room) and in the single I installed it on the bulkhead in front of the footrest. I had to cut holes in the deck but it ended up very neat in both cases. The pipes come with neat escutcheon plates. I mounted the switches on the decks also. I used switches with a rubber booties. All parts are standard and obtained from local ships chandler, except the rechargable batteries which I obtained from a battery outlet. They also had a recharger as well. Get the really powerful pump...you'll be surprised how long it takes to pump out even when the jet of water is shooting 2' into the air!
The batteries are only small as well ...not car or motorbike size (actually about the size of a large cigarette packet) and can still operate the pump for many emptyings of the kayak before needing recharging. I mounted the batteries in the day hatches.
Hope this helps