Unless your pump-outs are different I never ran across one that needed "priming" and don't think it's possible. This things work the same as a vacuum truck or honey wagon in that the intake is not going thru a pump.
I've seen harbor patrol here chew someone out for not using dust collection systems with a palm sander. There's big signs all over our marinas saying "Dumping ANYTHING in the water is a crime". It seems an unnecessary and unsound practice to me.
"Just call me TB"