Welcome to the forum.
It looks like Butler Lake does not provide that service. A phone call to them might provide additional local insight.
https://www.cityoflakebutler.com/parksrec
Assuming your '98 250 Sundancer gets to the lake on a trailer, down a ramp, then the "easy" option is to use a campground for pumpout.
Or go out into the ocean off Jacksonville and pumpout into the ocean, complying with all appropriate regulations.
