I get my chlorine from pinch-a-penny in 2.5 gallon jugs. When they are full and I try to pour out into my measuring jug, I get chlorine every where.
Here's my solution. I bought a plastic faucet off Amazon that has washers and a locking nut, drilled through one of the spare jug caps and hey presto! Works good so far, but don't know what 10% chlorine is going to do to the soft rubber washers over time, although I'll only use the modded cap when I need to add CL. It needs a relief vent but I can't drill through the back of the jug, as I need to exchange it for a fresh one.