Flew on a US Navy DC-3 ish tail dragger in Iceland during the mid 70s. In flight ‘relief’ was in the back through the rear compartment door at the tail. On the back of the door was a funnel connected to a tube routed through the bottom of the plane....
Rickover did NOT want ANY urinals or toilets in the back half og the submarine (engineroom bulkhead to the shaft seals.)
Had several convenient (waist high) drain funnels leading down to the aft drain tank.