Is there a plumbers dye?

Trying to find a leak in bathroom. Is there a dye that the pros use that won't stain a tub? If I use a dye in the tub water then I will know when I see the dyed water on the unfinished ceiling below that it is probably the drain, not the pipes or mixing valve.

Thanks!!!

Food colouring will do fine.

If the leak stops, then it is NOT the pipes. There are easier ways to isolate whether it is the valve or drain, and a plumber would know how to do it.

To check for leaks in toilets, specifically flapper valves I generally use food coloring.
I would be hesitant to use dies in other locations.
Michael

I remember many years ago, the septic field police were going around to homes and flushing a packet of dye down the toilet. Then they would walk around the property looking for the dye to break to the surface or enter a stream.

Marina's do the same thing with boats, throw a die packet into the holding tank so they can fine anyone who pumps overboard!

Plumber's dye is what they use to dye the Chicago River green on St. Patrick's Day.

http://www.greenchicagoriver.com/story.html