There was a recent thread dealing with someone's oil spill that discussed the various approaches but for the life of me I can't remember what the title was.
I started it, can't remember the title off-hand either, but it's out there.
Some of the products I've been using so far are Dawn, Zep citrus degreaser, 409, and Kaboom. Some of the others that were recommended just weren't quickly sourced, I didn't want to wait for an Amazon delivery, etc., so I've been using that I could get my hands on quickly.
All of these have worked reasonably well, for what they're good at. OTOH, suds can be an issue. Anything that makes lots of suds slightly complicates the suck-up process, so...
I used the degreaser in the two bilge areas I can't really reach, lightly flooding those areas with diluted Zep concentrate, sucking, repeat... then lightly flooding with diluted 409 concentrate, sucking, repeat... then rinsing with fresh water, sucking, repeat.
Dawn has worked best as a diluted spray on vertical surfaces. It tends to drip downward, and collection with rags is slightly easier than using the vac, once the amounts are in control.
After treatment with products... I've gone over some of what I can reach with a steam cleaner and rags or a mop head, too. That seems to be a helpful step, too. Still have a couple bilge compartments to go, for that step.
I haven't used our pressure washer down there; it has a tendency to splash residue all over the place, so wanted to avoid that. Especially in the two "hidden" compartments where diesel flowed in and through but didn't get sprayed all over the place (sidewall and so forth) during the initial event.
-Chris