There's really no such thing as an "after tax" HSA. "Pre-tax" contributions are deposits into an HSA made by your employer, and those deposits never show up in Box 1 of your W-2 and are never taxed. "After-tax" contributions are deposits made by you with the funds coming from your (after-tax) checking account, but you get to take a deduction for those deposits so the effect is exactly the same as making a pre-tax contribution.
