The no wanking rule isn't because they're being PG, it's because of one of them gets horny, they want them shagging.
This isn't true. It's because it's legally considered a public place. And there are decency laws. It's the same reason as no nudity in the shower. It's a public place. There are a variety of crew members, producers etc watching them all the time, never mind the contestants, and they can't be expected to have to watch someone having a wank..
The toilet is private and they can masturbate in there if they wish. What they cannot do is openly masturbate where they can be seen by other contestants or crew/staff members.
To me this is completely and utterly reasonable.