I bought ferrules from eBay
but to use for fuel lines. Like these and from this seller
I know he is in UK, but you'll get the idea.
You could wire (stainless safety wire for example) the rubber hose onto the pipes on the oil manifold and filter presumably and slip ferrules over that perhaps.
But, I pinched a trick from someone else here and shortened the feed side pipe and use a clamp (not a worm drive) on the hose and undo that and slip the hose off to drain the oil. Very unmessy!! Doesn't get the bottom of the tank, but it works for me given I have a filter on it anyway.
Personally, I'd like the assurance it wasn't going to come adrift and spew oil all over my rear tyre.