I'm prone to having slow running pipes every 6 months or so. I think most women tend to have this problem. I have tried many, many things in the effort of keeping my pipes clear, but unfortunately in the past, my go to solution often required dumping incredibly harmful chemicals down the drain. Never one to back down from experimentation, here are a few natural & homemade methods I've used the with great success:
Stop Before It Starts--Most of my drainage issues have to do with my ever shedding hair getting caught in the pipes. Aside from installing a cheapo hair catcher in my drain, the most effective thing I've done is to brush my hair BEFORE I take a shower. This catches all sorts of loose hair & prevents it from going down the drain. This is also the only time I really can brush my hair, because brushing curly hair is an all expense paid trip to Frizzville.
Heat it Up--Pour boiling water down your pipes. I have to say I'm not entirely certain that this would help clogs, rather I've found it helps in prevention. Instead of boiling water for the sole purpose of dumping it out, I save the water after hard boiling eggs & pour that down the drain. I wouldn't save pasta water though because food particles could grow some funky stuff. Best to stick to clear boiling water.
Chemical Reaction--Use a combination of baking soda, vinegar, & salt to clean out your clog. The baking soda & vinegar will react with one another & foam, while the salt will scrape down the sides of the pipe. I've never precisely measured, I usually just pour equal amounts of soda & vinegar & finish with some salt. Allow that to sit for several hours, rinse with hot water & repeat if necessary. If you need measurements or more recipes look here.
Mario & Lugi's Best Friend--When nothing is seeming to work & you're about to run out & buy some NASTY chemicals, try a plunger first. I have no idea if a plumber would actually recommend this for sinks, but I am telling you, it has worked for me 9 times out of 10. You might need to be persistant, espeically with the bath tub, but it will work eventually. I had to plunge mine for about 5 minutes today, but now the pipes are running free & clear.
I realize that in extreme circumstances you might not be able to clear your pipes with these methods, but they are certainly a good starting point & could save you money & save our water ways.