I came across this and wondered if anyone uses it on their XJ8 with any issues?

Fumoto Valve | Qwik Valve™

Whats the problem with taking of the sump plug?

Also if the plug is fitted you will have to cut the under tray and have it poking out.
I'd be worried that an impact open the valve (even with the safety lock)

If you really want something like this my advice would be to fit one at the engine oil cooler

Add a t-piece to the cooler and the valve off that. Add a tube too the valve output to poke just out the bottom of the radiator undertray. I'd locate the valve behind the plastic cover on the right side of the bumper (next to the fog light)

PS not something for me though

Cheers
34by151

Its a neat idea, but I think a better option for a fast oil change would be one of those devices that sucks your oil out through the dipstick tube.

I have used one on my Jeep Cherokee since 1996. Great for a vehicle that you can get under easily. It saves on the splash when the drain plug is removed. It has been dependable and does not leak. I haven't tried one on the XJ.
DAVE