I have 22 2.5 gallon tanks i breed pods in and at least 10 5 gallon tanks.
I spend all the time thinking of ways to make water changes easier.
I have had the fluval edge and drilled the back for a fuge for my 180
Other then drilling the tank or creating your own overflow, the amount of water you put into the tank also has to return to the main supply.
Since you cannot drill or wont, and you dont want a big pump.
Sure the 3 gallon per hour is slow, but what do u want.
Even a maxi jet 100 puts out too much flow for the amount of plastic you can drill into.
If you could get a half inch on there and i know you cant, you would still overflow your fuge.
If you want to drill it with a 3/4 inch bulkhead i can say for certain a maxijet 600 works.
see my old fluval with drilled back.
http://canreef.com/vbulletin/showthread.php?t=64165