I too agree that some people take a ridiculously loooooong time dumping and it's discourteous to others. I know that many have to return their RV to a storage facility at the end of a trip, so the complete wash out is needed. BUT, there are many options to not blocking a busy campground, like using something closer to home, Camping World, some rest stops and other places that offer public dumping.
Luckily, we have large tanks and are set up to dump at home at the end of a trip, so no need to do a comprehensive wash out until we get home.
I've always liked the SaniCon which REALLY makes life easy. During the few occasions that we have to dump at a dump station, like Yosemite, I pull up, pull out my already connected 1.5" hose, stick it in the drain, pull the black tank valve and turn on the pump. All done in under a minute. Once the black has drained, I open the grey, within about 30 seconds, it has flooded the black tank with soapy grey water and I finish draining both. On the SaniCon there is no hose to clean. Just put the screw on cap back on and stuff it back in the water bay. The SaniCon takes about 4-5 minutes longer to drain, but less than one third of the time it takes for others to pull out hoses, connect hoses, disconnect hoses, rinse hoses (without spilling on your shoes) put sewer and fresh water hoses away.