Welcome to the forum
This subject has been discussed in several threads. If you search using "anti siphon valve" I'm sure you'll find enough threads to flood your senses.
Some replace the valve with a new one, some replace it with a brass one, some take it out and use an anti siphon valve at the exterior connection. What ever you decide, don't just take it out and call it good.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.