Copydex (aka cow gum though no cows are involved!) is the only thing I use.
Brush Copydex on the painting stick, position miniatures, allow Copydex to dry, paint miniatures, allow to dry, peel miniatures off the stick, peel Copydex off the stick - rinse (not literally) and repeat.
Available from Amazon, Hobbycraft, B&Q, Staples and many other stores in anything from 50ml to 500ml pots.