Hello,
2 of my favorite airtankers at Boise ID,BAe-146 T01 and T02,these have the internal tanks and i believe they are pressurized by looking at the 5 holes in the bottom,but the 5th hole might be for air intake ? the BAe-146/RJ45's of Aeroflite have external tanks,which ofcourse are gravity flow.they look pregnant though.