I have my own set of glasses that are exclusively used for my brews (Dad's beer glasses!). I rarely ever put them in the dishwasher or the detergent in the sink - I just give them a good rinse at the end of the drinking session under really hot water, ie, flash scald them.
Not only detergent, but kids using the same glassware to make Milo and other milk based drinks can really kill the glass when it tries to release bubbles from the microscopic imperfections in the glass - but lets not get too techo here :lol:
I find that using Dextrose in the priming (either bottle or bulk) helps make a finer creamier head than normal white sugar, plus you tend not to get the cidery aspects to the white sugar.
Perhaps you need to make the kits a bit more robust - one can and a kilo of sweetener won't necessarily make you a brew you can stand a fork up in!! Once I got a bit more generous with my recipes, including the use of wheat malt, things really improved. I'm speaking from bitter experience here!
Cheers,
TL