I think my breather pipe might be cloged with something, all of sudden the shower won't drain correct, it takes it about a hour or two to let all of the water out. I've run hand snakes down the drains and come back fine. the house is 50 to 60 years old and is all cast iron pipe, every p trap has it own breather pipe going up, and only one coming out on the roof. Dosn't seem to be a problem with any other drains. what is the best way for me to try and clear the breather pipes? Like I said I'm broke and would like to fix this myself. Thanks for any advise.