I don't take long when there's people waiting, but will be extra meticulous if there's no one behind me. I just bought a clear 45 bend with a connection for flushing the tank and to my frustration have found I continue to get more and more little tidbits out the more I flush the tank. After the first two or three flushes it's pretty much only little bits of toilet paper. If no one is waiting behind me, I'm for sure going to try and get as much out as I can. I estimate this might take 10 -15 or so, but I've never timed it.
Luckily, I found a place to dump near where I store my trailer and I've never had anyone waiting behind me. I can do a quick dump in less than 5 minutes near camp, fill the tank with some water and then do a thorough flushing before I put the trailer into storage.
If I'm going to be using the trailer again in the near future, would it be just as fine to do a quick flush, fill the tank with some water and let it sit until the next trip?