Loads for operating hopper/dump cars?

[Boyd]

I have some black fish tank rocks but they are heavy when they are in a hopper and they don't dump out well. What do you guys/gals use?

[Dannyboy6]

Try Scenic Express O Scale rubber ballast. $20 for a gallon size container. I use it in my scratch built tipple and although my O scale Lionel cars weigh a lot when full, it looks realistic and dumps fine.

I built an auger in the tipple that delivers the "coal" from a hopper behind the wall into the cars. It's controlled by a push button switch at the edge of the layout.