The return hoses are all low pressure and are most commonly secured to the pump and associated plumbing with worm gear hose clamps. After a while they will frequently soften up at the end where they are clamped, and should be replaced. The auto parts store will sell you hose by the foot and it takes about 3 feet or less, depending if you have the fluid cooler in the low pressure side of the line.
Each hose uses an O ring on each end to seal them. The hoses will swivel when they are installed and tightened into place. That is why there are O rings on the fittings. The O ring is the part that actually makes the pressure seal. If you slide the nut all the way back as far as it will go, you will see the O ring and the groove cut into the center section of the fitting.
Sometimes you will get some white Teflon rings with the pump or rack. The rings go on the threaded part of the fitting to reduce or prevent small leaks. They are not meant to seal the pressure part of the line or substitute for the rubber O ring. Heat the white Teflon seals in hot water and they will be easier to install. You can install the fittings without them and not have any leaks if the O rings seal good.
Purging the old fluid from the power steering system:
Buy several extra quarts of fluid to run through the system to flush it when you change the rack or pump. The car needs to be up on jackstands for the next step. Fill the pump up, start the car, and turn the wheels lock to lock to bleed the air out. Then stop the engine, disconnect the low pressure hose (the one that is secured with a hose clamp) and drain the pump. Re-connect, refill and do it several more times or until the fluid looks clean and not burnt or black.