Most residents of Allegheny County are intimately connected to a place they've never seen. But tomorrow, ALCOSAN holds its annual open house at its wastewater-treatment plant, along the Ohio River in the North Side.

ALCOSAN reports that thousands of visitors turn up for this all-day festival, which includes tours of the facility, free food and even plumbing advice.

I was there this past Wednesday for a press tour — my first visit — and have to say it was rather fun (even without the open-house bells and whistles).

The plant, situated on 59 acres about a 10-minute drive from the West End Bridge, can process up to 250 million gallons of wastewater daily. (It's an easy ride up the Ohio River bike trail, too.) Seeing the scale of machinery required to keep our drains cleared and our toilets flushing is a bit mind-boggling.

The event also includes games and performances (from Environmental Jeopardy to Gemini Theatre's "Little Mermaid's Pollution Solution"), a virtual fishing stream (with local snakes and amphibians) and prizes.

ALCOSAN is also trying to educate people about its efforts to comply with a federal consent decree requiring it to prevent discharges of untreated sewage into the river during rainstorms.

Or you can just check out ALCOSAN's Mad Scientist, who'll explain how microorganisms help to clean sewer water before it's sent back into the Ohio.

Appropriately enough, the event is rain or shine. And it's all free, parking included.

ALCOSAN is located at 3300 Preble Ave.

For more, see www.alcosan.org.