9.6 oz will make a gallon.

2.5 gal = 320 oz

320/32 = 10

so your dilution is 1:10

then you measure 9.6 oz to 96 oz of water.

if you want to make an exact gallon then measure 8.8 to 88 oz of water.

Yes, yes I know the end result would be 96.8 oz, but is close enough for goverment work....no?

BTW I should mention this is to go from your concentrated solution to your stock solution. I guess you then dilute the stock solution 1:9 to get the working solution. If you want to make a working solution from the concentrated solution you have to make a 1% solution which would be 1oz for for 99 oz of water.