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Oxfam GB have a desludging pump in their equipment catalogue. The code is WSDP/6, which includes generator, pump, fittings, hoses and anti-dive plate. The pump has a rated delivery of 20m head, and can handle solids up to 30mm diameter. Cost is, in the OGB catalogue, 3238 GBP.
There is a risk of collapse when using the pump in unlined pits, so you need to consider health and safety issues fairly closely-fencing while desludging etc. If the pump cannot handle the solids then you will have to add water to make a manageable slurry. You can use 50 gallon drums to transport the water in a pickup. Add the water to the contents of the trench and use a chain drag to agitate and mix the slurry. You can then use the empty water drums to collect the slurry.
Another option, unfortunately widely practiced, is manual desludging. As obnoxious as this sounds it may be the only feasible technical option. This needs to be handled carefully and sensitively, as there are often significant social stigmas attached. In my experience it is often carried out at night as the guys doing it don't want their peers to know who it is. This is a filthy, disgusting and dangerous job, so if you go down this route pay the guys well and provide protective clothing, full face safety visors, breathing masks, gloves and bathing facilities.
From a public health perspective it is critical to ensure safe final disposal. If these activities are not supervised very closely there will be a tendency for the people doing the emptying to use the nearest convenient spot to discharge to. If you cannot ensure that this will be done correctly, and it will probably be quite a difficult and time consuming task in your current circumstances, then it might be safer (and probably less expensive) just to back fill the trenches, space allowing. There is a very real risk of protests from residents in the area if they feel that he job is not been carried out properly. I have heard of several cases of NGO's and staff being targeted with violence due to spillage and poorly planned final disposal, though not in Haiti.
A final option is the use of bio-digestion powders. These are added to the trenches and reduce the volume of sludge in the pit. I have heard mixed reviews on their effectiveness and have no direct experience of using them. If this is a route you would like to try let me know and I will dig up some information on suppliers and effectiveness on Monday.