I do use Oxy, but I also use a bottle brush attached to a cordless drill. Bit of oxy solution in there, insert brush, quick 10 second blast at full speed, pour the oxy into the next bottle, rinse, done and ready for StarSan. I only use about 500ml of Oxy solution for each batch of about 40 bottles so you could just buy some bottled water to use for cleaning. Once my bottles are in use, I always give them a good rinse with warm water to remove the majority of yeast straight after pouring, saves having it get dried on. I still brush and Oxy as well, it just makes it easier.