When Wakko tries to go to the restroom at the gas station, the owner whom requires his patrons to use the key to get into the restroom admits he hasn't cleaned it for over a year then laughs at him. Technically, the owner would be fined by his local Health Department within days or weeks if any patrons report the restrooms having not been cleaned for the time being, alongside being infested with roaches.
In "Potty Emergency" after Wakko pulls out of his bag what looks like a toilet that he refers to as a "potty", he later uses it when he goes inside the movie he and Yakko and Dot were seeing. A toilet flush is heard. Toilets cannot flush unless they're hooked up with plumbing equipment in any housing facility.
The farmer in the first populated scene (Jigen) is supposed to be driving the ox cart, but isn't holding any reins.
Wakko would not have been able to fully hold his bladder (that's full) when going to Mt Everest and back into America. Mount Everest is located in the Himalayas in Asia and he could not travel to Mount Everest and back without taking a ship or an airplane across the Pacific Ocean.
When Wakko realizes he has a full bladder and needs to go to the bathroom, as he walks out of the auditorium at the movie theater, he is greeted by a sign at the men's restroom that says "OUT OF ORDER". No movie theater would be permitted to operate if the toilets/urinals in their restrooms were all out of order out of respect for patrons who need to use the restroom; since the purpose of having restrooms is out of courtesy to those who need to go, especially when it's urgent.
In "Potty Emergency", Wakko could have instead had a potty chair like what toddlers use when being potty-trained instead of what looks like a real toilet.