steaming pipes

okay drove it down the road to local shop told em what was going on they pressure-checked cooling said was ok i watched em they just put one of them pressure deals on the rad. will that check headgaskets to? they said yes they said since i've only drove it 600 miles in 5 years + keep it in a open carport that i might wanna drill a hole in the flowmasters to see if water is in them they also said that the condensation coming out the pipes was clear and the rad. full of coolant so thats noy the source is this correct? the flowmasters were on it when i bought it i've never heard mufflers holding water?