I found an iphone app that works well. AutoCrapDump
Install automatic trap door and leave the tank valve open. When desired, pretend you received a call and look like you are talking. Push OPEN and presto. Tank empties, discourages tailgaters! Multifunctional.
Seriously, I also am interested in how those automatic devices work over time without jamming or requiring maintenance. Let's hear from the users and believers.