Here's a couple photos from internet:

Edit: I think our plumber just installs 4" PVC pipe that he cuts a couple slots  (where pipe enters and exits) for curb stop. He cuts with a hacksaw, but then takes a torch and warms the pvc pipe and bends outward those two "flaps" (they will lay on top on the water line) and the remaining sides of pipe, go down beyond pipe (= it keeps pvc pipe centered , so your On/Off tool will get to the curb valve). He only sets on those "push-on" caps(on top) = easy to remove; but this last one was at the fenceline, so cattle don't bother it, and he just drilled a small hole in cap and left the On/Off tool (homemade with rebar) in that cap's hole, setting correctly on valve about 5 foot down.

 This was for a cattle waterer, near a fence. Top of pvc pipe sticks above ground about 6-8".

(31171big_curb valve wrench.jpg)

(drawingD_curb valve photo.gif)

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31171big_curb valve wrench.jpg (11KB - 1136 downloads)

drawingD_curb valve photo.gif (42KB - 1568 downloads)

m4_f8_curb_r30893.jpg (28KB - 1227 downloads)