I bought some water-based Texprint Mono inks from you for printing on cotton t-shirts. I also purchased a retardant gel to prevent early drying. But often, after I’ve used the frame and before stripping it, there’s a lot of ink left on the frame and even rubbing it with my hand doesn’t help to remove it. What might be the solution?

When working with water-based inks, prevention is always the best solution: the ink should never be allowed to dry on the screen, it needs to be cleaned away whilst still wet.

The retardant can help, but it's the screen printing technique and the speed of the screen printer that are key.

In any case, an abrasive sponge soaked with water can help to remove the dry ink:  even if it washes away some emulsion, this will only help the liquid stripper to work better.

Make sure you soak the sponge with water, not with solvent: with water-based inks the solvent just creates a sludge that's impossible to manage.