Originally Posted by Annandaler

There is no "customs" on an international departure (from BUF or IAD or anywhere). If you have a US visa with a foreign passport, the stub of the I-94 form that was attached to your passport on arrival here will be collected by Lufthansa before you board LH419.

You will go through standard TSA security at BUF. You don't touch your checked bags at IAD - United transfers them to Lufthansa automatically.

LH419 usually departs from gate B49. The 2pm United arrival from Buffalo can use gates in A, C or D concourse. A and B concourses are two halves of one long building. Similar with C and D concourses. There is no security check between concourses.

If you arrive at an A gate (UA uses A1-6 for some Express flights), you just have a 15-minute walk to the Lufthansa gate. If you arrive at a C or D gate, carefully follow signs for transportation to the B concourse - it might take as much as 30 minutes gate-to-gate.

Lufthansa has a lovely lounge next to B51 if you qualify for entry.