You should have a credit on your Frequent Fueler card for an RV dump. I don't know how it gets figured and applied, but I had one for $7 on 05/05 that expired on 06/04, and now another one for $10 on 06/03 that expires on 09/13.
From Flying J:
For our best customers, those that are members of Flying J's Frequent Fueler and RV Real Value clubs, a $5.00 dump station coupon will be added to their card based on fuel purchases. The club member must present their card to the cashier at the point of purchase to receive the discount.
I haven't bought much fuel at the J in the last few weeks. Been at home and mostly where Flying J's aren't, so someone with more of a recent history of fuel purchases might be able to figure out how many gallons of fuel it takes to get a $5 credit. Or, someone could just give 'em a call on Monday and ask.