SAN RAFAEL (KPIX) -- When it rains it pours, so the saying goes. But, when it rains a lot in the Bay Area, that pouring begins with sand poured into bags to stave off floodwaters.

And, as it turns out, there's a trick to filling sandbags: don't fill them.

"You just want to fill the bag half-way to three-quarters of the way full. You want to leave some room so you can tie it off and you also want to keep it easy to work with -- the more sand, the heavier it is," said Steven Coleman, with the San Rafael Fire Department.

Firefighters also say how you place those (partially) filled bags makes a difference. They recommend a pyramid-stacking system for fast-flowing floodwater.

MORE INFORMATION: U.S. Army Corps of Engineers: Sandbag Techniques