New Post of thanks to those who offered help 8 months ago & and solution for everyone. Problem- 110 yr old Victorian, upstairs 2 tile showers, side by side were installed upon a 12" raised platform in mid 1950's. Before I replaced the 1 1/2" drain pipes from the hubs, I wanted to prolong hubs life. Showers used 6 months of the year so I had time. Throughly brass-wire brush old rust and swabbed clean. 1st coat,'Sprayon' zinc rich galvanizing compound (used by USAF, USN etc). Product lasted 20yrs plus on saltwater boat trailer. 1 can applied to both. Top coat, 'Hammerite' RustCap(encapsulates rust). Looks like new today!
Ventilation a problem- use swimming snorkle, a garden supply connector to several feet of ribbed tubing, larger diameter than snorkle. Or duct tape. Hang intake outside shower and breath through your mouth. Also works great when working with paint remover.