I think I have it working... At least, it hasn't blown up yet!
EVIL ENERGY 1/4" 6mm Non Return One Way Check Valve for Fuel Line Oil Petrol Diesel Aluminium Silver Pack of 2 https://a.co/d/j9GIcsj
OTUAYAUTO Universal Windshield Washer Nozzles Kit - Replaces OEM #47137, Spray Jet Kit (pack of 11) https://a.co/d/eygY2Ea
I kinda eyeballed the location to mount the spray nozzle on the camera housing and then hot knifed the nozzle to trim off the extra "booty" extending past the housing. Eventually I'll paint it to match the body. These nozzles are adjustable and I was able to direct the stream across the lens despite being very close to one another. Surprised and happy about that!
The hard part was getting the siphon issue resolved. The check valve in the link did eventually work, but I needed to modify it a bit.
The spring inside is very very weak, so I bought the spring assortment from home depot and found one that was a good fit and put enough pressure on the diaphragm to stop the siphon. However, that only worked until I tested the washer because the pressure popped the cap off the spring. I solved that by putting another spring on the outside of the cap, because the valve body has about 3mm of space between it and the cap.
That held, but it still dribbled!! So, I added a small washer between the spring and the rubber diaphragm. I think it helped distribute the force on the seal. So far, so good. It's not so strong a seal that the spray is compromised, and by placing the valve an inch from the nozzle, only a very small amount of fluid is able to leak after using it.