Quote Originally Posted by mgb74 View Post
...gravity hasn't failed us for many, many years ...
It has on occasion here in earthquake village.

Back on topic, I'd go with a 5-gallon bucket containing float switch-controlled submersible sump pump. Not too expensive and mighty convenient. It could empty through a clothes washer drain hose. They have a U at the end to hook into that 4-foot high wall drain pipe.