I just got the CG. What I did was everything you mentioned, but I had Haato lick Toru's butthole three consecutive times (after buying the costume) and got the CG. I think it's supposed to be a continuation of the other CG, the one where you lick his butthole.
Sorry if I explained it badly. What I meant was I got both the CG for rimming Toru and the maid costume CG just from having Haato lick Toru's butthole 3 times. If you got the rimming CG on your current playthrough, you'll probably have to restart the game and buy the maid outfits first.
I got it the first time I made Haato and Toru go to the hotel together. Toru was a submissive bottom.