Tub cleaners are not disinfectant though and that's what he needs to do to keep down the bacteria. Bacteria is what has caused this and since it's running rampid in the rot infection it's true you need to keep this better than hospital clean. Simple bleach dilutted to water 20:1 bleach part being the 1. If it's possible get two of the same tub and that way you don't have to stress her by holding her while you disinfect the tub. You can set up the disinfected tub put her in it and then switch them daily. That way it's not as much work and stress on both parties. When you disinfect the tub use hot water and dilute the bleach right in it and let it sit for 20 min. Then wash it out really well, and let it dry in a safe place so it doesn't get dirty again and switch it out the next day.
Ps do this while she's got the rot. After get chlorhexidine. And dilute that with water and keep it in a spray bottle. It kills bacteria and can be used around the animal. When mine poop in the tubs I take out the affected bedding, take a papertowel, spray on a bit of the chlorhexidine and wipe up the poop of the tub. I use bleach 1 a month when I disinfect.