I took it apart. The piece that bolts on from the left (you can see that piece in my earlier picture, bolted onto the valve from the left) is supposed to - I think - press the left pipe tight into the valve. However, the piece simply slides of the pipe on the left. It is not tightening anything.
When everything is bolted as shown in the picture, I can simply grab the valve and pull it to the right. A gap between the valve and the left pipe opens up as shown in the picture.
I don't know if anything fell off over time, or perhaps the piece that bolts onto the valve from the left was attached to the left pipe but broke off ...
Can anyone look at their grey tank valve assembly to see how the left pipe bolts onto the valve?
Thanks
It's broken. The pipe should be permanently attached to the bolted square. You'll probably have to hacksaw through the pipe at a convenient place downstream. The replace the left side broken part and ABS glue the new piece to the existing cutoff pipe with a coupler.
