Bleeding off some fuel ?'s

I have a 19 gallon pump and only need about 15 gallons right now (we'll need it all later). I'm plumbing in a checkvalve/hispeed between the shut off and barrell valve and looking to bleed off about 25% of the fuel before it gets to the hat. What size pill should I start with and do I sit it at the same pressure as my idle check or ?

thanks