Yes, it's biodegradable and safe to put down the drain. I do it all the time in my brew room. Bosco is correct here - using it to clean grill grates is a different application and you get a really nice oil slick on top of the water. So, if you pour it down the sink or toilet, be prepared to wash off the oily stain that's left.
While they recommend using gloves, it's basically because in a commercial brewery, which is where this stuff was developed, you're cleaning much larger pieces of equipment, so your contact time with the solution is much longer. I generally don't wear gloves in the brew room, as I'm not in much contact with the solution and rinse it off as soon as I'm done. I wore gloves when I cleaned my grill grates, mainly because it was seriously greasy/yucky water, not so much because of the PBW. YMMV