If you can fill this yourself, or persuade a male friend to do it, you deserve some sort of prize.

I don't know if I could get away with running a contest like this, and then how do I select the winner?  Do I have to test somehow that it's really been done, and the bottle is really full, and it's genuine?

I don't really want to think about that.

Shouldn't have made this bottle design really.

Eurghhh..

Bit late now, people seem to like it so I'll carry on selling it for now at least.

Maybe you should buy one, and fill it with something that looks genuine, and leave it in the bathroom for guests to wonder about.  Maybe they'll have a sneaky sniff or a taste, just to check.  They know if they don't, they'll always be wondering.

Or if you can manage to fill it that would be the ultimate prank for your visitors when they 'check' it.