I just ordered a 3/4" "bilge fitting" from www.skidim.com
for $26. I have a 2 pump system on my boat and at first I had both pumps coming off of a T from the stock bilge hole, but I ran into priming issues. I have decided to put each pump on their own hole and found that skidim was much cheaper then other places.
One thing to keep in mind (if you buy Tsunami pumps) is that you may need to cut the threaded shaft of your pumps shorter (like to 1" long) so that they won't have priming/clearance issues.