Section 1926.51(c) is the federal sanitation rule for construction. Table D-1 counts employees and sets toilet seats and urinals, not units, so ask whether each unit on a quote includes a urinal before you count it as covering both.
Temporary field conditions
Under 1926.51(c)(2), even temporary field conditions must have at least one toilet facility available. A short job isn't a reason to skip it.
Sites with no sewer
Where sanitary sewers aren't available, 1926.51(c)(3) allows privies, chemical toilets, recirculating toilets or combustion toilets, unless local codes prohibit them. That's the rule a standard porta potty meets.
Mobile crews
Paragraph (c)(4) says the toilet requirements "shall not apply to mobile crews having transportation readily available to nearby toilet facilities." A crew that works one Brooklyn address for weeks doesn't fit that description. OSHA has also written about how close "nearby" has to be; high-rise porta potty rental explains that interpretation for upper-floor work.
Washing facilities
Paragraph (f) adds washing facilities for crews using paints, coatings or other harmful contaminants, covered in the handwashing station requirements guide.