I have a 1.5 gallon and I don't do full water changes. I use a gravel cleaner to clean the gravel (obviously) and take out about 50% of the water. And I put my betta in a seperate cup (like the cup he came in, if you don't want to buy a new one). I just fill the cup with water from his tank and then put him in it using a net. That way I don't accidentally suck him up or anything. :P Then I add water to the top and put the conditioner (and I also use aquarium salt but it isn't neccessary).