I use the cups that the betta came in from the petstore when I bought them. I scoop them into the cup at water change time and put the lid on the cup. Then I give the tank a thorough cleaning and the gravel as well. I then put the tank back together and fill with aged dechlorinated water that is the same temperature as the water was in the tank before. I float the betta in the cup inside the tank for 15-20 mins, then I release him into his tank by submerging the cup and letting him swim out. They are minimally stressed this way and the tank gets a thorough cleaning.