In the Arctic, toilet visits are allowed during hikes. In Antarctica, no toilet visits are possible on land (per Antarctic Treaty / IAATO regulations). If you have a frequent need for the toilet, you should take a bottle (e.g., Nalgene bottle with a wide opening) or another field toilet option on the hike.
Please note: Oceanwide Expeditions does not provide field toilets. You can make your hike easier by not drinking too much beforehand. During the hike, only drink when thirsty.