Sorry. Got confused about what was being cleaned.
I find a nailbrush and elbow grease works on shower tiles too, and a wipe down with an e-cloth after a shower (it's only after my showers as no-one else does it).
A wee squirt of mould killer on the sealant that you can't scrub works well and won't destroy your septic tank bacteria. As jess says, the quantities of bacteris in a septic tank will be huge. It'd take a lot of bleach (like a big slosh every day, which is not necessary in any circumstances) to spoil the, ahem, septic soup.
Good Morning Wednesday 24th June 2026
Needless to say I haven't tried that.