I'm thinking of getting a Bosch C 1050 ES LP condensing tankless water heater. It is recommended that if the PVC exhaust is longer than 6' horizontal that you have a condensation drain in the exhaust vent. The length is going to be closer to 15'

The only condensation drains I've seen for 3" venting are stainless steel.

Can I use pvc snap T to make one ? and am I correct that the trap that the drain is connected to is what prevents the exhaust from coming through the drain ?

Or are you supposed to connect the PVC to the stainless steel condensation drain units.