Well... Other than the periodic getting too distracted to notice the tank is full, I haven't had any accidents. I have 2 ends - the ubiquous gravel vac, and a "special end" I use most of the time. I used to, when doing the w/c, lower the glass on the end so it would stay in the tank. Shortly after getting my eheim, I was eyeballing the u-tube and hit upon an ingenious solution - attach one to a section of tubing and use that for w/c. It works. Just hook the sucker over the tank rim. It isn't going anywhere.
I'm still using the original valve I got with a tetra set some...12? years ago. It actually works better than the Lees I picked up a few months ago for the siphon used in my kids' tanks. Now... I did have issues with adaptor/faucet incompatability which lead me on a trip to Lowes for a special adaptor for the infernal faucet (confound price pfister) and while I was there, I picked up a portable dishwasher quick disconnect.
My mind is aglow with trancient nodes of thought, careening through a cosmic vapor of invention - Hedley Lamar