It will probablyt be ok, but the worst rust in under the normal
standing water. My 50 year old 4 inch pipe was so rusty a snake wouldnt
fit thru there.

Just sop you knpow the condition I would use a wet dry shop vac to
remove the water, and take a look, that pipe is likely less than a inch
opening it the other piece rotted off.

its a lot of work but can be replaced DIY with plastic, that will never
rust