According to archaeologists, in Britain, as many as 40% of Roman military camps have preserved traces of latrines. The most famous toilet is the one made of stone in Housesteads, England, at Hadrian's wall, which could accommodate more "military". This type of latrine was most often placed close to the place where the hill fell (the Romans located their camps on elevated terrain), which enabled the natural outflow of waste, relative hygiene and removal of bad smells.
We also know that there were smaller latrines, intended for the command staff or a single unit of contubernium - numbering 8 soldiers. In the case of the latter group, the latrine was probably located in the front part of the tent (the so-called arma).
It is difficult to estimate how many latrines were needed to serve a Roman fort. Everything depended on the period, diet and way of life of the soldiers. Recent research, however, comes with interesting information. It has been estimated that a soldier ate about 850 g of wheat a day. If the grain was ground, it came out that he ate 760 g of flour.
Assuming that flour has about 11 g of fibre per 100 g, and it is currently recommended to eat a minimum of 30 g of fibre per day, it turns out that the Roman soldier had a very healthy and high-fibre diet. Based on this knowledge, we can estimate that he produced 250 g of faeces and 1.24 litres of urine per day.
So, taking into account that the army consisted of 30,000 soldiers, we find that it produced 7.5 tons of faeces and 42,600 litres of urine per day. To put it more visually, in less than a month, a football field would be covered entirely with 3 cm of faeces, and an Olympic swimming pool would be filled with urine up to a meter deep.
However, it should be borne in mind that the army also included slaves, servants, and animals (horses, draft animals). Researchers indicate that Roman horses, 1.42 m tall (smaller than their modern counterparts), produced about 11.7 kg of faeces and 7.6 litres of urine per day. If we assume that a single stable could accommodate 3 horses, it turns out that the animals there produced about 75 kg of pollutants per day (including straw bedding), which formed a several-centimetre layer on the ground. So it was necessary to get rid of the material on a regular basis.
Researchers suspect that the Romans may have dug ditches that served as latrines, e.g. in the intervallum (a space of 60 meters between the ramparts and the first rows of tents). In order to flush and drain the excrement from the hill, stones were used, which were placed in the drains. Sometimes the impurities had to be removed manually; for this purpose, soldiers, captives, or slaves may have been assigned to perform such duties. It is also possible that various types of utensils or containers were used for defecation. A large vessel that could serve this purpose was a dolium ceramic container, which was placed in the ground and leaned against the wall, thus serving as a potty.
It should be mentioned that the Romans were extremely practical, so it is possible that, for example, urine was collected and used, for example, to clean clothes, and sometimes even themselves (the Celtiberians supposedly used urine to clean their teeth). The droppings, in turn, could be used as kindling to the fire.
Taking into account how big a problem it was to clean the camp of all impurities, it is practically certain that many soldiers took care of their needs "wherever possible". The stench level could be truly incredible. Ancient sources even mention that enemy reconnaissance was able to sniff out the enemy camp from afar.