We each paid 280,000d for a sleeper bus back to Hanoi, directly from Sapa. The seats were almost reclined and the layout was bunk bed style in rows of three and ails in-between. There was no toilet on board but we did have a small bottle of complimentary water on each of our seats.
We set off at 6:30pm and had a few too many stops in-between, not for the toilet but because the tourist buses in Vietnam carry cargo to various destinations and usually have to wait around for the owner to collect it. This definitely adds a couple of hours to the journey time and we arrived at Hanoi bus station by 6:30am.