As Rick mentions, at the major train stations you pay to use the bathroom. The concession is run by an outfit called McCleans and they do a very good job of keeping the joint clean and tidy as attendants are constantly at work.
As you enter, you have 2 options. One is for standing, the other for sitting (think about it for a minute and you'll figure it out). Standing is 1.5 CHF, sitting is 2. There are turnstiles so you can't just waltz in, you will need the proper coins because the turnstiles don't make change (look around and you'll see a change machine). It looked like the gates would take either Euros or CHF. Men, note that you can't start at the standing side and walk over to sit, you have to exit and start all over again.
Also note that in some situations, like restaurants, there is often no charge for men to stand but all must pay for the privilege of sitting.