"Water overflow water loss" Installing valves on them, is not the brightest thing to do. Someday you will forget and the tank will burst or collapse and don't say you won't because you will.
The best way is pull them up and have them vented the same height as your Fresh water fill. Or better in your fresh water fill there's a connection for it (they used it for 50 years). The cost is no more than those one or two valves but is a lot safer.
Why RV manufacturers started to change to the low overflow beats me but was a stupid idea. Also when filling you will get the syphon effect which already let you loose some water before you even get on the road.
"Pay me now or pay me later" changing a tank with an underbelly is a lot of work believe me.
2014 Ram 1500 CrewCab 4x4 5.7 Hemi 3.92 Rear and Air Lift 1000
2005 Jayco Jay Feather LGT - 29Y GVWR-6500 lbs.
Pro Series 1200 lbs. WDH with Double Sway Bar.
Champion 3100/2800 watt Inverter/Generator-Onboard Solar Power
ALJO 'Forever Young @ Heart' provide on their travels Music Entertainment to Senior Care Homes