My Safari's drain valve has to make a half turn, from open to close. I cannot turn it using my fingers, so I made a wrench for the tank drain valve. I cut a 1/4" x 3/4" aluminum bar about 5" to 6" long, short enough to rotate the valve in the limited space but long enough for me to get a grip. I cut a slot centered in one end of the bar, the length x width to match thumb turn on the valve. Now it is easy to turn, using the wrench. But it's still hard to reach it behind the wheel.
2014 Silverado 1500 5.3L maximum trailering package (yes, I'm towing the 34')