1. To pour down (from or into something) in large amounts. The rain is positively sluicing down outside. I could hear the gurgle of the water sluicing noisily down the drain in the bathroom next to my room.

2. To clean or rinse something with a large flow or stream of water. In this usage, a noun or pronoun can be used between "sluice" and "down." The boss told me to go sluice down the stables and put down fresh hay. It's an old filmmakers' trick to sluice down the roads when shooting at night—they show up much better on film that way.