I have never used them for dumping but I often fueled there and have spent the night as well. They are like most other high volume stations...some are easy to get into and others are not. Best bet is to check out on Google Maps for aerial view. As far as spending the night, that too varies. Some have trailer/camper spots and others have just the truckers area, which can be rather noisy unless you are running your AC.
I have a Good Sam membership and enjoy the discount on gas so I'll usually check them out first. Honestly, just for a quick overnight, I prefer Walmart...quieter.
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