What to use depends on your maximum pressures. My processor is all hi/volume low pressure. 1800 Lbs maximum. It is plumbed entirely with schedule 40 pipe and standard plumbing elbows same as we had done on the farm for 50 years before I could read on the Internet that it would blow up. Yes, in spite of the PSI ratings and internet lore you can do it and it is much cheaper to run pipe and short hoses than long hoses, LOTS cheaper if you shop for fittings. I bought the 3/4" pipe in 10' lengths and cut and threaded it in the shop. Fittings came primarily from Ebay box lot sellers. Be aware that there are some very poorly made fittings around, all are from China but some are OK, some are garbage. Luckily the garbage is easy to spot, avoid it.
NOW READ THIS. Do not use schedule 40 pipe in you splitter or other circuits where you are running higher pressures. You can price our both Schedule 80 pipe and hydraulic tubing for that. Fittings for tubing can sometimes be had cheaply on Ebay, otherwise they can add up quickly and cancell out savings over hose. Standardizing on size helps a lot