I use external filters and when I got a new one I had a lot of trouble getting the pipes connected to the hard plastic bits of the inlet and outlet fittings and the tank connections as they were so tight.
I was given the following tip by someone at the lfs. Take a cup or heat resistant container and fill 3/4 with boiling water, then dip the tip of the pipe in it for about a minute. This will make it go softer and will be much easier to get the pipes on and also gives a much tighter connection when it has cooled back down so is less likely to leak.
I have also found it can increase the life of suction cups. I have found the suction cups on my ehiem internal seem to flatten out and not stick so well after a while. Dipping them in boiling water also seems to help them reform to there original shape and stick better.
Sorry if this has already been posted, I did have a look back but couldn't see it mentioned.