This has disaster written all over it.

No it doesn't.
There is only a washbasin and a shower connected to this outlet and they
won't be run at the same time. Also, the joint is clearly within view of
both so if it fails it will be spotted promptly. I'll be looking out for
it to do so, anyway. IF it does fail, then it's only a quarry tile floor;
no wood to worry about.
This is just a temp. bodge for a couple of days in my own house where I'm
the only inhabitant so please don't get hysterical.