I'll second all of the above - One way valves are particularly prone to getting small bits of seaweed, sand etc under the valve seat - they never close properly, esp if you go and find a nice beach somewhere....
The one advantage of trunks over bilge pump is that trunks don't rely on battery, a motor, a level switch etc etc to work (also see previous threads on reliability of them) - momentum & gravity are pretty infallable! The down side as said before - trunks are as good as useless unless you're on the plane.
Trunks can have the "pull up" string led forward to a cleat by the console, so you dont even need to get off your seat to fix them up!
Try these (in no partuicular order other than how they fell out of Google) for a start:
, scroll down to item HEN002063