How to clean dropping spots off of pontoon boat leather and flooring?

We just got a boat and it was never kept covered but was in a boat house. There are so many droppings on the seats and floor. I used a pressure washer and it didn’t remove a single spot.

My next plan is soapy water and a scrub brush but seems like if a pressure washer didn’t nothing that a scrub brush wouldn’t be any better.

Is there a secret method or some sort of boat safe cleaning solution that will help remove this grime? I believe it’s mostly droppings from bugs and spiders.