@Zereous It's been tried and does not work as well as you'd hope.

Durability is the keep issue.

well then again it can have a lineing like inside of the silicone like rubber bands and some Vynal squares or something or just streight Vynal that forces water out after Filled and if you want you can open it to become larger if you unconnect some plastic connectors inside so it expands a little more..
So its water filled with Shower curtain like material then it has a Silicone Layer

So they just make it and put a Vynal sack or a Plastic sack inside that will stop you from putting to much water inside so it does not pop.. SInce we are inventing this or whatever lol!
i suggested this to flashlight a long time ago they like.. they tried to make something like what i was describing without me but there's popped and so they wnt out of bsns

what happens when there is ignorance of the original inventor like they dont care who thought of or designed it

like if it was designed by me and some people interested then it would be designed to let the water preasure the Vignal area and the slit would not just be a hole but like an actual real like vignal shape so it would be elongated so you can move up and down or the other 2 ware you can move your member a whole inch left or right and it will slide without thrust.. So like as real as real gits basically but they just go and make it! get sued lol pdx or something but yeah..

if people want to design this i wouldn't mind trying to make this with some people its just like.. i dont know whare or how

@Zereous Reminds me of the water bed.