Off site motorhome toilet contents?

Flutel

I am currently on a break in an apartment building in La Manta Del Mar, in Spain. Walking around, I see lots of motorhomes parked up by the coast, obviously enjoying free and easy camping. It looks fabulous. My only concern is what happens to their toilet
contents. There are no beach toilets around, that I can see. I suppose I am worried that some people might just dump it in the sea.