No more than 20psi. The one that looks like a bug sprayer is a pain to use. There is no swivel so screwing it onto the master cylinder requires turning the whole thing around and around to keep the hose from twisting. And when you do unscrew it from the MC, the hose and cap and MC are FULL of brake fluid. Very easy to spill some. And you must clamp the overflow on some master cylinders so it will pressure up.

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MB-less