I have three valves, each pointing down at a 45 degree angle. Onee for the black, one gray and one crossover from the black. I did get a little leakage from my black tank valve, about a cup's worth) but solved that problem when I bent the push rod on a rock requiring a replacement. (about $20 from ACE Hardware) Solved leak.
A half bucket is definatly WAY too much seepage. If your valves are opening while you travel then you have a defective valve. If you're still under warrantee, have you're dealer change them out. If you are past warrantee, it's a "sort-of" easy fix. Drain your tanks first.