How do I list, identify, my a thrift savings plan account?

[maps4you]

Spoiler

I believe your TSP (aka 401K) will show up as a pretax deduction assuming you are not enrolled in a Roth IRA. The amount of wages withheld should show up on your W-2 in Box 14 with a letter code. I you are taking payments from your TSP account and your payments are tied to pretax contributions you will have to pay tax on those payments.  If you are simply adding to your TSP (not at retirement) you do nothing. The IRS will catch up with you when you start receiving payments FROM your TSP.