Welcome to the forum.
No mention of what year your XT 276 Toy Hauler is.
When hauling two Harley in the garage, I fill the fresh water tank between 1/2 to 3/4 full. That increases the tongue weight as the fresh water tank is about 1/2 way between the tongue and front most axle. In fact, I normally carry 1/2 tank of fresh water for 'on the road' bathroom use.
Also, have never experienced a sway issue .. loaded or empty. Then again, I have an Equalizer hitch with built in 4 way sway control. Try one, you will love it.
The Equalizer hitch has won the #1 award for best WD hitch for the past 5 years by thousands of readers of 'Trailer Life' magazine. https://www.equalizerhitch.com/
As for the outside spray washer, mine is a simple "T" off the lines that run to the bathroom sink.......no separate shut off valves. Also, I never use it as it's pretty useless IMO and has hardly any pressure. And yes, I have removed the outside shower 'box' and the lines are not kinked or blocked.