To remove the cap, I would first try a pair of needle nose pliers and wedge into the cap and remove. If there is nothing to grip,I would drill two holes into the cap. About 3/8 inches deep. Don't drill all the way through.(you don't want a bunch of shavings in the tank) Use needle nose pliers or stick two screwdrivers in the holes and use a third to turn it backwards. Make sure you drill into the plastic only. (no sparks)
1998 Pace Arrow 35 ft. F53 Ford V10 2012 Honda Civic toad
15 year motorhome service manager. 3 popups....2 travel trailers....5 motorhomes....loved them all.