So does the black tank flush on the Sunseeker have jets on it or is it just a way to fill the black tank with water without having to flush the toilet? I know you’re not supposed to run it with the tank closed but I did put water in it and water did fill up about 1/3 of the way but I never heard anything spraying inside.
If it is the same as on the sister to yours - we have the Forester 3051S - then I believe it has nozzles inside. I can hear what sounds like a slight whining noise when I flush ours.