SS:
Re this and other question.
Running the engine is irrelevant. If you don't clean the pre-filter - aka - the water separator (does both) - the engine isn't going to run anyway!
There is a big knurled thumbscrew which holds the glass bowl into a stirrup. Unscrew that and carefully remove the bowl with plastic element and spring. Also be careful not to lose the rubber sealing washer which fits between the top rim of the glass bowl and the metal housing. This washer/seal is important - if it is missing, air will get into the fuel system and bleeding will not eliminate it. (And engine probably won't start). You can wash out the plastic element with diesel or petrol or some other solvent. The end cap on the element can be prised off to allow access to the inside. A old toothbrush is handy for cleaning this element. Make sure the plastic element is put back with the hole facing upwards! Refit and tighten thumbscrew by hand - do not use any kind of wrench! You now need to operate the lift pump (with your thumb) to fill the bowl etc and fill the fuel lines as some diesel will have leaked out.
It may be possible to do this from underneath if you have a garage pit.
As for the main fuel filters you won't be able to get at those from underneath unless you are a contortionist. I would usually disconnect the fuel lines to the filter housing and unbolt it from the engine and then change the filter elements at ease on the bench (very fiddly to fit O-rings etc otherwise) - especially if you can't tilt the cab. The filters themselves are Crosland 522 or Knecht KX23 - for the Ford 110 hp engine. There are numerous other manufacturers who make equivalent filters. They cost about £4 or £5 stg in motor factors I would guess but you can get them for less on ebay.co.uk. - plenty of suppliers who will take credit cards, paypal etc and post them out to you - no hassle at all! Note that you need 2 of them. They come with O-rings as part of the kit. Replace all of the existing O-rings - even if they look OK.
Suggest you look at www.FordCargo.org - some photos of that pre-filter and cross-references for filters and also sources of parts which may be helpful.
Finally don't forget the air filter while you are at it. A new set of fuel and air filters is always a good idea if you have to go for an MOT - the air filter in particular is important for passing the smoke test! (plus a small amount of petrol in the diesel tank!!).
Keep On Trucking!
JD
March 2010