First of all we don't pump, we dump...
I have asked for permission and the same time I explained that I had filtered the waste water going into my tank and if the car wash wanted I could filter it as I dumped. No problem No charge as long as it was filtered and we didn't leave the bay a mess when dumping.
Most Car Washes get charged for the water they use not their waste water so by us dumping there is not charge to them.
Some car washes filter and recycle. These might have a problem with you dumping..
Thank you Terry, Yes we do get our truck washed at the same time. In the atomated ones I dump before we get cleaned.