A Staten Island pol says the city has such a suspect history of unnecessarily flushing away money on capital projects — including a projected $6 million bathroom facility slated for a park in his district — that he’s pushing new legislation requiring agencies to be more transparent about how they’re spending taxpayer dough.

Council Minority Leader Joseph Borelli said he will be introducing a bill at Thursday’s meeting that would require the city to post large signs at construction sites of its capital improvement projects.

The signs would be updated at least monthly and identify the actual project under construction, expected costs, the city agency handling oversight and other information to help the public track possible cost overruns and delays.

“People need to be more outraged by how much things cost,” Borelli said. “The [city’s] capital procurement process is fundamentally flawed. Despite lip service from previous administrations, nothing significant has been done to help the process.”

Borelli said he’s been shocked in the past by how much some projects wind up costing, including a bathroom facility he convinced former Mayor Bill de Blasio in 2017 to greenlight construction on at Seaside Wildlife Nature Park in Great Kills.

It was originally slated to cost a whopping $6 million, but could now wind up costing taxpayers even more — up to $10 million, according to the Parks Department’s website. The comfort station has been designed, but its construction timeline has been pushed back at least a year because of the pandemic with a builder yet to be chosen.

In the meantime, the popular park continues to have no restrooms — forcing some to resort to extreme measures.

“People go home or find a tree,” quipped Borelli. “Either we pay the vig to Park Department for capital costs, or people are stuck pissing behind a tree in perpetuity.”

Borelli also plans to introduce another bill on Thursday in a bid to create a new 15-person task force whose mission would be to reform the city’s capital construction system.

The task force would include seven council members, five mayoral appointees and the commissioners of the Buildings Department, Parks Department and Department of Housing Preservation and Development.

The Parks Department has a long history of coming under fire from critics for overspending on bathrooms, including $2 million spent to build a 400-square-foot restroom at Gravesend Park on 18^th Avenue in Brooklyn that opened in 2017.

A Parks Department spokeswoman said the agency “look[s] forward to reviewing” the legislation once it’s introduced.

The suspect spending extends far outside city parks.

Last week, some council members were floored at a budget hearing after learning the FDNY is seeking to build new kitchens at some of its firehouses — at a cost of $1.2 million apiece.