Cleaning the underneath????

[Survivor 69/Z28]

Hello!!
I hope this is not something that has been posted over and over. I did a search, but did not come up with anything.

I am looking for the easiest way to clean my floor pans and really everything under the car. Oh, my car is totally unrestored, I just want it clean. I have already had the car on a lift and took a very high pressure power washer to it. Sure it helped, but its still not near as clean as I would like it. I can take a rag and rub back and forth with force on my floor pan and it will be kind of nasty in about 2 seconds.
SO, is there something I can spray on the undercarriage that will do the work for me? Then I just hose it off.
Or is it best to use soap and water and just scrub the heck out of everything. Probably a nasty job, but I am up for it. Any tips would be very appreciated!!!!

One other point, not trying to remove rust. Just 38 years of deep down dirt. I would rather not remove any paint underneath as well. I want it pretty, but not freshly painted restored pretty if you know what I mean.


Thanks for the help!
Anthony