Can anyone recommend a washing powder that actually works on tough ground in dirt? My daughter helps at the riding stables and her T-shirt's are filthy! The dark ones must hide the stains as the light coloured ones are just disgusting. We wash at 40 with a good dose of surf/ bold etc usually whatever is on offer and I've tried adding vanish but not any better. I'm reluctant to wash hotter as worried they will shrink...