My old 5th wheel required me to get down and crawl under to reach kitchen sink valve. I was looking to add electric drain valves but ended up with a new 5th wheel instead!
They make extensions and eBay has them
12 inch extensionAlso electric drain valves
Drain MasterBarker DrainsEither of these could probably solve your problem as well
Good luck and happy travels!
Dave
2013 2500HD Chevy LTZ 6.6 Diesel Ext Cab Long Bed
2017 Grand Design Reflection 27RL 5th Wheel
Dear Wife, plus two Cocker Spaniels and a Standard Poodle