When I arrived, it was after dark. There were no street lights, and the buildings themselves had three 25watt lamps to illuminate their 10 rooms.
There was no obvious system and no sign-posting. Just present your Carnet to anybody, and they'll introduce you to the appropriate person.
I was taken down some stairs and through a courtyard area in complete darkness, to a locked building next door. The customs officer (presumably off-duty, judging from his jeans and T-shirt attire) unlocked the door by the flickering glow from a match.
Inside the room, and now on the fourth match, a candle was unearthed from the back of a drawer, stuck to the desk, and lit.
Their Carnet ledger was then completed, along with my Carnet (incorrectly until he was put back on the right track).
While the customs officer was spreading ink, a cricket was providing the cabaret by repeatedly jumping through the candle's flame.
Following a firm handshake with (presumably) the Customs Chief, wearing a beaming smile, I was sent on my way with the instruction to enjoy Bangladesh. After finding the truck again in the pitch darkness outside.
Driving away, I wondered why they hadn't stamped my visa with an “entry-date stamp“.