I haul everything from bacon fat to soy bean oil to salt water. Most places I unload. The shipper loads 99% of the time. The biodiesel places always unload. All I do is open the manhole sometimes.
I loaded and unloaded 100% of the time when I was hauling spring water. The hoses were provided at the facilities, so it was easy. Just hook up and load or unload.
Everything I do(dedicated account) is loaded by the shipper and 80% of the time I unload. We have many other accounts that are no touch on either end, We have some accounts that we load and then just drop at receiver. I kind of have an easy job, Dedicated tank( same product) load out and return empty
With the company I recently got on with, generally the nastier the stuff in the tank is, the less likely you're unloading it yourself. Most of the hazmat is unloaded by the costumer. Like if it kills instantly upon inhalation or eats your skin upon contact. Nonhazmat just depends on the place. Like someone else said here its about 50/50.