I have a slow shower drain. Home built 1950's. Has many vents on roof, probably has one dedicated to the shower. I tried sticking in one of those manual drain snakes that are 1/4" in through the clean out in the bath tub but it only goes in about 2 to 3 ft and goes no further. I pulling nothing out when retract the snake, but notice that water drains faster. So it continues to drain good for one day, then slows again. Any ideas, tips, suggestions, advice will be greatly appreciated.