Looking for ideas: a vacuum break for a water tank

I'm going to put a stick of 4" PVC on the roof rack that can be filled for water when camping.  I'll cap both ends and install a hose bib on the back.  Filling it should be easy if I fab up a female-female piece of hose.  Connect it to the hose bib, open the valve, fill from a garden hose.

Problem is, I'll need a magical vacuum breaker that goes on the top of the pipe that can operate both ways - let air out to fill, and let air in as I use water.  The main challenge is to keep unwanted things out - bugs, bird poop, mud, etc.

My first thought was a break from a frost-free hose bib, but they seem to only fit in frost-free hose bibs.  There are thread-on breaks with 3/4 hose thread, and they'll let air in, but not out, and they won't do anything about debris and junk getting in.

Is there such a thing as a two-way break?  Something that would open for inflow at low pressure for when I'm draining and pop the other way at let's say 5 psi going the other way when filling?

I suppose it could be two different valves.  Help me brainstorm some stuff.

ball valve

In reply to VolvoHeretic :

I'm trying to find something a little more automatic.  I dont' want to have to open two valves just to get some water, especially because it will be 8' in the air.  I don't really mind it for filling, I suppose, but I gotta think there is a more hands-off solution.

Also not sure how I would keep mud wasps, bird poop, and bugs out of the inlet.

Air admittance valve with a manual air vent right next to it?

You do not need it to hold any pressure at all, right?

Ultra-cheap: there are various styles of breathers or pneumatic exhaust mufflers which are made from sintered plastic or metal.  Obviously high flow, would keep chunks out but maybe not ultra-fine particles.  Maybe add a loop of tube (like a rollover vent on a fuel cell) to keep water from sloshing out while driving?

Less cheap: there are breather vents which use an expanded PTFE membrane (i.e. generic for GoreTex), also available as stick-on patches like you see on headlight enclosures.   IDK about flow rates, I could see this as a problem.  This would be the perfect thing if you believe Gore's marketing fluff about letting vapor pass but not liquid.  Used on paddle boards.

ZHYLING Waterproof Vent Plug Screws, Ventilation M8 M16 M20 IP68 E-PTFE Nylon Breathable Valve Pressure Balance

Guess you could use 2 one-way check valves with filters on the exterior exposed ends - one to let air in when draining, one to let air / water out when filling.

https://www.amazon.com/mxuteuk-Aluminium-Universal-Adjustable-M-H-032-12mm/dp/B09C7ZSZTD/ref=mp_s_a_1_41?crid=3P3L1LVX9LY7Q&dib=eyJ2IjoiMSJ9.hHwlQf1Hm4YsRq3NCu_ubJojKYEER7yqMrIET8zI28VmG796c2YRfUXXO3zy0_hSjYma3qvfWplUp3NMhaWBUStWI4ZDZU7RMtexls89Ml0CJrtpvHGs8o6Uv3JRV3dDsOivtWMOCsBGHP6EswsmeCaAOBK5LauslKR9Gang5a5HndiAfUtnuqFJpnWiXpr3Wr5gPKloeBdw41jcglLmOw.WFRSteQxsfYAk_xsLt1SPO_TIC4QqrN0HLMtuYrJ64s&dib_tag=se&keywords=breather+check+valve&qid=1709691823&sprefix=breather+%2B+check%2Caps%2C203&sr=8-41#immersive-view_1709691927491

In reply to Oapfu :

Those were exactly what I was thinking when I saw it..

I think you're looking for one of these.

https://www.dripdepot.com/guardian-air-vacuum-relief-vent-inlet-size-three-quarter-inch-mpt-pressure-check-no

We use them on drip systems to push air out of the system during fill and to allow air in to let the system drain when the pump turns off.

In reply to bearmtnmartin (Forum Supporter) :

Neato!