Your Pressure relief valve is there in case the system develops a blockage or such like , the valve the returns the oil pressure direct to tank.. or when you hold the trim button down and the leg is on the ground, the valve was already working then..
I deal with Phoenix all the time and they are good to me.. Not dealt with the marine side of things but should imagine are just as good..They supply all my needs for parts for my Hydraulic tanks that i build.
May i suggest an aircraft type long rangefuel bladder, if someone is flying a small plane over an ocean for delivery to a customer they often fit in a tough flexible fuel bladder inbetween the seats and run bypass fuel lines. Giving vastly extended ranges.. on a small plane we are talking 3-4000...
Please check for a fuel supply hose has not collapsed with age or excessive vacuum . The inner liner in rubber type hoses has been known to collapse with age and cause a perfectly good looking hose to not let fuel flow..
Please check that your fuel supply line if it is rubber has not had the inner liner collapse with age or vacuum from the tank to the lift pump. Possible causes a filter blocked causing excessive vacuum , making the liner inside the hose to collapse. or just plain old age..
How small or short a hose (3/16 bore to 1" bore) do you want??? I will make it to any length you want.. Stainless or carbon steel?? 1/8 Bspp to 1" Bspp, metric, jic,