Welcome Jeff! I believe the horizontal tanks can have valves replaced at a propane dealer, as well as recertified. Is it a permanently mounted horizontal tank, or just a portable horizontal?
The switch by the bathroom door is probably for the bathroom ceiling light. Turn on all your light fixtures in the bathroom as well as the switch. Then turn the switch off to see which one it is. The lights themselves have switches on them, but it's not a three way with the wall switch. If the wall is off, the light won't turn on regardless. If the wall is on, the light can be turned on or off from the ceiling switch.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR