What size thru hull fittings should I use???

[Christopher Quast]

Hey guys just wondering what size thru hull fittings I should be using for my livewell overflow sytstem I put the 3/4 OD ones on that I had and I tried it and I'm not sure it will keep up with the incoming water from the pump when I tested it I used a garden hose wide open, and it kept up barely. Will the pump have more or less GPH flow rate than the garden hose the pump is an attwood 750 GPH

[sparcebag]

From reading and thinking of installing one the overflow recommended was 1 & 1/2 inch,and I have a 500 gal pre hour pump.