This is a Hallett project I recently started. My first jet boat. Building not buying. Not that I don’t buy many other things.
   I used a trowel shovel and a shop-vac oh and a 8 year old. She filled the trash bags.  Hope this stuff wasn’t toxic. Took me 3 straight hours non stop and filled 5 trash bags and the city trash can. Had 7 inflatable bags in there too. Only a couple still had air. 1970s air. And something else in there. Looked like a paint can but nothing really left. And a paint stir stick. There was blue on what may have been a lid. I really dont know. 
   Anyone thinking of doing this it’s a dirty job but just get in and do it. It’s mindless. Trowel worked great.  A bit slow but less of a mess compared to a pressure washer.