A few years ago, prior camper, a prescription pill bottle fell from the medicine cabinet, right now the toilet. Well, I lost the medicine and wondered about the bottle. Never did notice any difference in dumping my black tank. We had 3 weekends in a row with full hookups after that.
Then the 3rd week-end I added some water to the tank before coming home because I wanted to give it real good clean, lots of giggling and sloshing of the water. At home, I caught the black tank contents in a bucket and dumped it down my clean-out (city sewer hook-up).
To my surprise, the pill bottle went Ker-Plunk in the bucket (yes, on the 4th dump since it happened). I fished the bottle out of the bucket and of course, threw it away, and then dumped the bucket down the clean out.
The best I could figure, the bottle had air in it and it must have sealed pretty good. Of course a bottle with air will float in liquid. So I suppose, it continued floating on the top of everything and maybe somehow stuck to the bottom of the tank and then didn't have water to help pass it through. By adding only a couple gallons of water to slosh around, the sloshing must have sloshed the bottle into the neck of the drain pipe, so when I opened the slide, it fell out. Evidently, the drain pipe held more than just the 2 gallons of liquid.
But it did come out.
A bottle cap will pass through with no problem. If you really want to catch it, then drain your contents into a bucket and watch for it to come out. Thend dump the bucket, one bucket at a time.
Now, about a year ago, I was dumping my blue tote down my septic tank. And the black 4 inch cap fell into the septic tank in my back yard. I thought ... oh no! I have more caps, that's not the problem. All I could think of was that cap passing through my finger system and clogging up.
I watched in desperation as the thing floated on top of the sludge in the septic tank. I was going to get a shovel, or the dog pooper-scooper and try to retrieve it when it tipped, and down it went! That hard plastic did not float, thank goodness! Its now sitting in the bottom of my septic tank. I suppose the next time I have to have the tank pumped out, I'll have to let the guy know there is a cap down there so it won't clog up his honey-dew wagon system.