leaking black water tank

Here is my update on the problem and the repair.
After removing the strap that secured the elbow, I could see that it was loose and rotated with a little bit of twisting. I eventually worked it out with gentle twist and pulling. The other photo shows the white plastic (nylon or polyethelene) sleeve that comes out of the black tank. That was very securely attached to the tank, probably glued, and with a spongy neoprene like filler that was put in to stabilize and minimize movement of the components and keep out bugs and critters. As best as I could determine, the leak happened because that white looking substance on the elbow no longer had any properties to seal/adhere the elbow in the white sleeve, hence since I could easily twist and remove it as it wasn't doing it's job any more. My T@B is 6 years old(I'm the third owner) and we have been using it hard in the 2 years we've had it. The issue than became what to use to reattach everything. 3M Marine Sealant and Adhesive is a very aggressive product along with Loctite Marine Sealer/Adhesive( half the price of the 3M). Once these products set there is no way to undo it. I wanted something that would allow for a test of the leak but could with some effort allow removal to redo the repair. Finding something that was compatible with two very different plastics was a bit of a challenge but my local hardware recommended a neoprene sealant used on commercial/residential windows, so I bought the Master Seal NP1. It is a high end industrial grade sealant that is not considered an adhesive. It has a very high flexible quality when dry and is a superior grade product. I applied a decent sized bead around part of the elbow that has a ridge that stops the elbow from sliding to far into the sleeve. You can see where the original white stuff kind really didn't make it to that point. After sliding it into the sleeve whatever oozed out I used my gloved finger to smear it around the seam. I waited 24 hrs for it to skin over than tested it and saw no leaking. Next was what to use to fill the void space around the sleeve. Again it had to be flexible and water resistant. I settled on Total Pond "Water Fall Foam Sealant". It comes in a spray can like the yellow stuff people use around electric outlets and plumbing to keep air from entering your house. This was another neoprene based product. The only issue is that it has to held upside down when using which made it difficult to apply to the void space around the sleeve. Eventually I got enough in to finish the job. I reattached the metal strap and made sure it was snug against the elbow to minimize any movement from traveling and dumping the tank. So far the repair appears to be good, I'll update if necessary but I feel confident this will work. The bonus is that I saved a lot of money doing it myself. If the leak would have been around the sleeve where it is attached to the tank, it would have required pulling the toilet and either pulling the tank out or using an epoxy sealer to eliminate the leak, again another costly repair if you can't do it yourself.