Sedimenter is a good place to start, you'll find it on the inside of the chassis rail on the drivers side, over the rear axle.
It has a plastic screw in the base, don't try to force this as it will break! If the screw doesn't undo easily then just remove to complete bowl and clean it.
If the sedimenter is also clogged with muck then it may be worth removing the fuel tank pickup though the access cover in the rear floor.
If you do these two then give it a couple of days and then put another new fuel filter on. ;)
One other, relatively cheap, option would be a new fuel lift pump as these quite often go and are only about £20.
