I remember hydrogen peroxide from school days and it was stinky stuff.
I use phosphoric acid diluted down to about 10% in a spray bottle. Wash fermenters out with dish detergent (very small amout), then lots of hot rinse water , then boiling water, then spray with the acid and put lid on till ready for the brew.
I spray all tubes , taps etc with the phosphoric acid prior to bottling/keg filling.
Also after washing out kegs , I add boiling water and some acid , seal keg, give it a good shake, then hook it up to the gas and beer lines and pull the whole lot through. Cleans keg, lines etc
So far so good.
Another plus is that phosphoric acid is a food for yeast so, I reckon my yeast get a head start in the fermenters that have been sprayed with it before the wort is added.
My 2c