Do Atlanteans all go doodoofeces in the water? How do they wipe afterwards? Why would anyone want to go visit Atlantis if all of the Atlanteans soil the water constantly?

Seeing as they are not human the first question would be if they even have to do these things or if their body's cleanse themselves of waste in an entirely different way. 
Never have seen any mentioning in any comic Namor has been in that they even excrete and urinate like human beings. 
 
And if they did need to I highly doubt that they just do it in the water or that they would allow their waste to be pumped into the Oceans water seeing how they are highly protective of keeping it pure and clean.

and he says humans pollute the sea, pffft, what a hypocrite

Atlantians are smart. They probably have some sort of restroom system down there. 

There aren't many differences between the sea and air. I mean, landfills are that way and I try to stay over here where the land and air is fresh. I mean, how can us humans walk around with all this smog, fumes, and other air pollution? Including that as a result of that body function. Its all about how concentrated and potent the build up is. The ocean is a huge place, more sea than land after all. So Namor basically does what we do, but just a bit different. How different? Well time for the imagination hat! 

I don't blame Namor.  When you're surfing in 52 degree water, peeing in your wetsuit feels gooooooooooodddd.

@Rheged: Lmao his face on the last panel. 

I doubt they get all that uptight about it. Fish are going to poo in the water even if they don't so it's not like it'd make that much of a difference.

The bathroom, huh?

He probably uses it the same way anyone else would;

1. He walks in
2. He closes the door
3. He uses the toilet
4. He wipes his arse (if necessary)
5. He washes his hands
6. He leaves the bathroom.

like a fish.........

Poop everywhere... EVERYWHERE.