Well, removing the check-valve on the potable fill port does not work. There is a 1/2" hose connected to the check-valve via a screw-on PVC fitting. Something else would have to take the place of the check-valve. Besides, a 1/2" hose is not going to large enough for a 1/2" fill-tube for the gravity fill, since the tube has to fit inside of the connection. It seems like a good solution would be a bladder or chamber that could be filled with the bleach solution, and that would fit inline with the hose and the fill connection. Then the water could push the bleach solution into the water tank as the water goes through the bladder/chamber. This is one ridiculous non-feature of a travel trailer that I have ever seen. I am thinking that drilling a 3/4" hole into the potable water tank from the top of it is a better solution. I will search for ways of sealing the plug online. Thanks....
2015 Forest River Wildwood X-Lite 241QBXL
2007 Red Ford F-150 XL Pickup truck