If the ink is flowing freely to the waste ink tank bottle then this shouldn't happen. If it did happen despite the free flow of ink, then I wonder if you forgot to insert a small vent hole in the lid. All the kits I've seen have this. Without it there's a risk that you'll pressurise the waste ink tank and the ink won't flow, in fact it may get pushed back.
The Octoink Printer Potty does have some sort of one way valve. I just emptied mine and checked. For those that haven't seen them, they're a low-profile retangular container, and the inlet port is towards the bottom on one end. Thus the inlet port needs to be one-way, to stop ink banking up in the tube as the tank fills, and to enable the tank to be disconnected for emptying without the waste ink running out. Between this valve and the crimp on the tubing, emptying is simple and straight-forward.
Works pretty darn well. Generally I get most of my printer hardware from IJM, but these waste tanks and also the Octoink SquEazyFill bottles are so well designed and thought-out, while being simple, and the service is so good, that they're two of the few things I'd endorse without any reservation whatsoever.
---In DigitalBlackandWhiteThePrint@yahoogroups.com, <rdeloe1@...> wrote :
You should install an ink waste tank so that the printer doesn't fill up the waste pad and die an untimely early death. And you can make your own to save some money, but if you do, make sure to use a check valve between the line you install and the printer's waste ink line. Because if you don't install a check valve, you're going to wonder why your printer makes a mass of inky bubbles at the capping station during the ink change procedure...