britpart aint the best.....
you have a number of choices, depending on what you have tackle wise, and how much messing about you want to do....
# buy a delphi pump and try that.
# refit the old pump and perform the test again. less/more bubbles and you still have a lift pump issue, but confirms probable knackered new pump. same amount of bubbles, either both pumps are dragging same amount of air in, or theres another problem.
# test old pump off the motor by rigging a couple of pipes and holding open ends under diesel level in a jam jar. note any bubbles being pushed down from pump to diesel. (needs decent fitting pipework, useful to have a couple of old pump pipes for this)
# same as above but with new pump
# closer investigation of fuel system once pump is confirmed ok.
# remove boot crapet and floor inspection cover to check pickup pipe from tank.
# bypass sedimentor if you cant get it in bits. precure an 8mm-10mm push on airline fitting, a 8mm-8mm fitting and 6 inch of 8mm tube. snip the olives off and use the push fitting to bypass the sedimentor. remove the sedimentor housing from chassis and poke all the crud out. my guess atm is its got a pin hole in it.