There should be drain pitcocks on each tank's bottom side. I would also check for a air filter drier system and have it serviced. Once you have started the engine and it has warmed up a little you can increase the RPM's to 1k to help in the time needed to fully build up the air pressure.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7