One of the reserved openings in the iron sewer pipe of the bathroom of the old house should be that

Sell what you should have, remove the old one, replace it with a new one, and be careful not to damage the rubber pad!

The iron ones are gone, and they should be replaced from top to bottom and replaced with hard plastic ones, so that they don't have to worry about rotting.

The sewer pipes of old houses are all iron, and the cover of the observation port is generally the surface of the iron is rotten, and the iron is anti-corrosion. This kind of sewer pipe fittings manufacturers do not produce, if you want to damage it with more than 3 thick iron plates to make one, anvil two flange eyes, and install a rubber pad on the pad.

Find a professional person to repair it, don't fool around, break it and spend more money.

This is the cover of the access opening on the sewer pipe, which is sold and can be replaced. You can buy it directly by going to some plumbing equipment stores, which requires you to have a good cover sheet specification in advance, and you can use it if you buy the same model, which is very convenient. Of course, if you are afraid that it will corrode and rust again, you can buy a stainless steel coverslip, and now there are also replacements, but the price is a little higher, of course, once the stainless steel is replaced, once and for all, it will never be broken again.