Tub Shower Magic (Dawn White Vinegar.) 1:Heat vinegar in microwave until hot and pour into squirt bottle. 2:Add the Dawn soap. Put the lid on and gently shake to incorporate. 3:You now have a powerful cleaning product that will melt soap scum and tub and shower buildup, clean sinks, appliances and just about anything. Just spray it on, scrub, rinse and be amazed. For tough soap scum build-up, spray the mixture on and allow it to sit as long as overnight. Then, scrub and rinse.