If someone empties / changes his/her colonostomy bag, should s/he say "Asher Yatzar"? I would assume, yes, as this is the person's method of ridding waste. I assume the same answer would apply to someone doing dialysis? Or, is the bracha limited to only the "standard way" of "going to the bathroom"?
One with a colonostomy generally has 3 excretions per day and should make the bracha of Asher Yatzar after each excretion. Nishmas Avraham (ed 2) Orach Chaim 7:1;note 7)
Rav SY Elyashiv, Rav SZ Auerbach and Tzitz Eliezer write that he can only make the bracha after cleaning and covering the area. Nishmas Avraham (ed 2) Orach Chaim 76:9;note 7)
See pg 24, fn 230 here for an English discussion by Rabbi Dr Avraham Steinberg.