Don’t know how to describe this!!!!

I have a Diplomat ADP8322 dishwasher that I have had for quite some years now. It doesn’t get used a lot, maybe once or twice a week on average. There has been a problem with it for a large part of that time but it appears to be getting worse and it’s beginning to drive me crazy! There is a grey pipe that comes along the floor of the machine from (around) the middle and then goes up the back wall. I have always assumed that this was the pipe that takes water to the top spray arm. When you first turn the machine on it’s fine but after about 15/20 minutes the pipe pushes itself out of the socket on the machine floor. It then starts making banging noises! I have pushed this back in and it used to rectify the problem but, as I said, it seems to be getting worse and now just keeps kicking itself out. It almost appears that there should be some sort of rubber grommet or something holding this thing in but I have never been able to find out anything. I am asking you guys if you can help, otherwise I think that the thing is going in the bin. Appreciate any advise that you can give.