They're not actually in the plumbing. They're coming out of wherever they are hatching and are crawling into the plumbing looking for moisture. To eliminate them in the plumbing, you need to eliminate them from where they're really emerging. Often this is an annual problem for a couple of weeks around this time of year. How long has this problem been going on?

Thanks, Its been 2 months. We are in Alexandria, VA. So its on and off warm from January, on. They must be emerging/nesting between the walls/floors. They are immune to the usual poisons. Last year we had good luck with Borax, but this year they just rub there hands and drool in anticipation. I think the regular spraying around us has made some super bugs.

This is the plumbing forum, however, we give lot's of off-topic help too.

I believe that Kudzu is correct that they are looking for water.

If you are concerned about pesticides, I would use boric acid (often sold as roach powder). It is a fine powder that you use by blowing into cracks, behind cabinets, into wall cavities, etc. I have purchased it in a squeeze bottle or I've seen it applied with a squeeze air-puffer.

The powder is tracked back to the nest and kills all of the ants or roaches. It works through dehydration and therefore isn't prone to insects becoming immune.

There are various recipes for home-made ant bait on the web that include sugar and boric acid.

It is typically considered safe for humans. It's used to treat fungal infections such as athlete's foot, jock itch, and various other issues.