Basement Bathroom Plumbing Check

[Reach4]

As for the Backwater valve I have seen them on whole houses that didnt require one One would think it be ok but not the case

I figured 3 was as small as those would go.

I am not saying that you would want one for the upper story.

For the lower story, you would not want one with a flapper. Those always leak. You would want one that is "normally open".

Overhead sewers are the best for avoiding sewer backups.