I can't begin to tell you how many people share your sentiments regarding purchasing an enema bag in person at a pharmacy or elsewhere. It's a very common shared reluctance.
A combination bag is usually the most convenient for personal home enema use, but restrict it for enemas for yourself only. For sanitary reasons, don't use it for douching or share with a partner. Buy a separate bag (preferably a differnt style or color) if necessary.
If you can't get to that Walgreens link directly, just go to http://www.walgreens.com and search for enema.