During the RV manufacturing process all kinds of things get into the holding tanks: dirt, sawdust, plastic plugs (shown here),
Plastic piece found in holding tank
electrical wire pieces, screws, bolts, staples etc. These items should be blown out of the tanks prior to water testing, as some of them can stick to the bottom of the holding tank.
This particular piece, came from a hole saw falling into the tank during tank assembly. Unfortunately this plug made the tank, drain very slowly. It was found in a 3” elbow after the Drain Master valve. This same plug can get caught in the tank outlet before the valve and the result, is the RV owner thinking the valve is not working because the holding tank is full and will not drain.
I had a similar thing happen years ago. I called Drain Master and talked to Dan because I thought my valve wasn’t opening. He troubleshot it with me and we figured out that a similar piece of plastic was left in my tank during manufacturing. I figured it was my crummy luck. Guess I’m not the only one. I wonder if pieces like this are left in holding tanks often.