They make trailers that are complete washrooms. Multiple sinks and toilets in stalls/single toilet and sink with running water. Also, they're heated. Septic truck comes every so often to completely service them.

It's child's play.

We live where there is no municipal water or sewage. We have two holding tanks, one for water, one for waste. We haul the fresh water ourselves, but there are contractors we could hire. We call a pumper truck to empty the waste water tank occasionally and they haul it to a municipal dump site where it gets treated along with the rest of the municipal sewage.

There are RVs all over the place with appropriate toilet and water systems.

In the early 1980s, I worked at remote work camps with wash shacks that had hot and cold running water with flush toilets.

It's a solved problem.

There are already trailers that are self contained washroom units. Some sites already use them some just have portable toilets.