Need rec for level indicator freon receiver

[haze10]

For an R22 Horizontal Receiver, about 22" diameter. Need a recommendation for a continuous level indicator. Primary concern is reliability, and leak free design. Can be electronic or mechanical. Any ideas.

 

[rmw]

I have seen bullet type sight glasses used on the side of tank. The tank was for F-12, but that is how the liquid level was detected. Liquid visible in the bottom glass, good, top above the top glass, bad.

rmw