Is it the grey pipe at the back which keeps popping out?
If so then you need to replace the filter cover. As on there are locking clips which do break so it doesn't hold the spray arm tube in place. Its quite common on these Whirlpool dishwasher for this to happen.
Click here for the part you need
Replace this and that will cure the fault and stop this from happening.
If you need anymore info just get back to me.