Most motorhomes can go 3 or 4 days before needing to empty their grey and black tanks, although I am aware that there are a number of irresponsible ones who park up for months without moving. As a former GA property owner and now motorhome owner, I can see things from both sides. I wouldn't want to see a total ban but I'm sure that a restriction to a max of 48/72 hours, perhaps with a nominal €5 Euro a night charge might resolve matters.