The practical thing to do is do like me. Use 6 changes - tre in qiuck succession first, the 3 successions interspersed with TV watching and coffee drinking (a joke I develop films with cofee.....), usually I end up with one or two changes of water for good measure, yoiu know water in the tank before hanging the film, and add two drops of detergent in that last water.

I do this because it suits me, is convenient and because I like a cup of coffee after all that inversing, shaking & rattling a tank!