We recently moved from Tucson up to Payson AZ. Half a mile from our new home is the Giant {brand} gas station right on highway 260. For more than half of the year theirs is just about the only dump facility for a very long ways. They catch all of the traffic coming down off of the Mogollon Rim {where the only two dump stations are closed from October through mid May}. In so doing they do sell a lot of gas but their prices are in line with every other station in town.
On weekends their dump stations are packed, often with a wait of 30 minutes to nearly an hour. When my 24'Class C needs to be dumped or if i just want to flush the tanks I go up mid morning/mid week and have the place all to myself... and yes I do buy gas there. This works very well especially as I really did not want to be dumping into my septic system at our new house. I have never spent more than ten minutes in a dump station and 5 minutes is the usual but my black and gray tanks are only 20 gallons a piece. Time spent is more a function of knowing what you are doing vs volume but get behind a 45'+ DP and see how long they take. ;)
Lots of folks seem to assume they will be able to dump before leaving their campground but often it is not practical. Busy campgrounds typically have long lines/waits {especially on Sunday's} often due to the incompetence of the folks trying to use them... really people, it is not that complicated. Also due to the heavy use I have often seen CG dump stations out of order/shut down for extended periods of time.
Now the folks who can't or don't want to wait are headed down the mountain with an extra 40 - 60 gallons of "stuff" adding 400 - 600# to their rigs, which often are already near or at their GVWR's. Something to think about in the next "discussion" here about actual weights in the real world. :S