We have a Jayco Eagle and have the same issue except it is about a quart of liquid. I have twist on cap with a clear elbow. When I go to hook up sewer I connect to RV park side first. Then i just simply hold sewer hose under cap and release slowly to drain in hose. Then connect to RV I never spill or get any on myself. Just part of having two gray tanks and black tank and long pipes after gate valve. Once I figured out how to do this it's no problem but it use to really bug me, now not even a second thought.