i either go swimming (with a tampon) or lay in the bath for an hour or so (with nothing) let the water in and push it back out. I did this and period SLOW'D down very fast... I was changing every 15-20 minutes with leaking too...before i got in the bath....so water helps me!!
I also found water helps. Laying in the bath (for 30 to 60 minutes or so depending on your situation) really seems to work well. A doctor I know also suggested showering might help as well. Another way I've found that works for me is rest. I've noticed that it seems to be heavier when I don't get enough sleep or if I'm stressed out. Try relaxing and making sure you get at least eight hours of sleep.
I have been doing this for as long as I can remember. I have very heavy bleeding but bathing slows it down... I don't know how, but it does. If I am close to the end of my cycle, a long bath will even make it end sooner.