just a "thinks" struck me , would you not want to keep the poo , as post flood most good soil will have been washed away and so large amounts to soil inriching fertilizer ( poo) would be valuable to restart farming once the land is dry .
i mean the plants did not go in two by two . so the seeds will need a good start to grow in time to feed the ark's zoo once the waters are gone and the zoo is free to roam .
true BUT the neutrients will have been wash out and disolved into the water , so are much more likely to end up in the oceans / seas /lake post flood that on the land , and look at the land around mt arrat not very good looking to start farming on ....
i am assuming no massive seaweed growth during the flood , and as we do not know how deep the water got after covering the last mountain , can we assume it was mt everest ?? at that time , very deep water will mean massive water pressure and zero light at the land s level
also considering the range of animals in the ark some poo couls have been used as fuel for heat / cooking /drying etc .. some poo and urine is used in cloth and leather working , again a stock could be built up , until the animal where free and could repopulate the land and provide for the people .
maybe the orginal ballast of the ark could be dropped over the side and the poo packed down as new ballast to store until needed .
Alo given that all would be eating dried stores from the arks food supplies the amount of poo per day would be less as time passed , dried food taking longer to digest ......