I've tried using sodium hydroxide (NaOH) to clean mold (mould) in the shower before on a patch test area, and it worked really well. This simply involves using drain cleaner (with gloves, open window etc.) liberally on a scourer, and just wiping it on the tiles, plastic shower pan etc. I waited for ~20min, then used the shower head to spray it down the drain.
I understand that NaOH is highly corrosive and would easily eat into the skin, however it is intended to be used as a drain cleaner. Thus presumably it's OK on plastics used in pipes such as ABS and polypropylene.
Qs: Are there any gotchas (unintended side-effects) that I should be aware of with this method? Is this OK to use on silicone and grout?