150' Main question

Not sure where to post this Q.
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Let's say we have a 1" city water tap with 100 psi at tap. Then 150'ft. run to house with 10% uphill grade.
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What pipe would we need for the least amount of loss in psi and GPM?
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We have a 18 GPM tub deck faucet with 3/4" flex tubing line to it. We are trying to ensure 18 GPM at tub.
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Builders plumber w/ 25 years exp. claims he doesn't know the answer. Is why we are asking you.
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Thank you

It depends on what kind of pipe you use. But friction loss for Sch 40 PVC is a good rule of thumb. You would have 8.6 PSI loss per 100' for a total of 12.9 PSI loss in 1" pipe. With 1 1/4" the total would be about 4 PSI loss, and with 1 1/2" pipe you would only lose about 1 PSI.

There is nothing the pipe can do to make up for the elevation loss. You will lose 1 PSI for every 2.31' of elevation from point A to point B. The best you can do is install larger pipe so you lose less to friction loss.

When elevation and friction loss combined cause more loss than you want, a booster pump is needed to increase the lift or pressure.

Thank you valveman.
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It would seem that 1" tap at city connection then 1.5" pvc with least friction loss is the answer. Which pipe would have the least resistance?
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House has 3/4" flex tubing running to filter system that reduces another 5-6 before traveling another 60 ft. to tub. So total run from city tap would be about 275'.
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Elevation is about 20 ft. rise including run through attic. Yes, the contractor/plumber didn't run correct line under slab foundation. He later came back and ran 3/4" flex through attic to tub.
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The attic run with 9' ceilings may have cost us another 20 psi.
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All other plumbing runs through Manoblock.
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Thanks

What is 3/4" flex tubing? Pex or Poly? Or something else?

3/4" flex tubing with crimp connectors they are using in new home construction now days.
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Not sure of material but white in color.

I'm not a Plumber, that's why I ask, I'm not familiar with all the new piping and their fittings. I do know some pipe is physically smaller than their cousins. Like PVC has a much larger ID than CPVC. This all adds to your friction loss.

A run up to the attic doesn't cost anything if you bring it back down to the tub. The part that goes down with counter act the part that goes up.