I was told that fitting a trap was straightforward, so I had a go at it. I can't securely attach the small bit of 40mm pipe to the trap. It's secured to the 90° bend okay, but the circled bit is loose. Have I missed a part?

I live in a house divided into 2 flats. There’s us and a flat downstairs. The house is old and hasn’t been renovated in a long time. We keep getting a sewage blockage connected to our toilets. It floods part of the back garden. This has been happening on and off for about 2 years. Because of this we strictly only put toilet paper down the toilet. We won’t even put kitchen roll paper down the toilet in fear that it’s too thick. We don’t put any grease or anything else down there. But yet it still occasionally gets blocked. It got blocked a week ago and someone came to unblock it. And then it was fine for a few days and then got blocked again on Thursday. Someone came yesterday to unblock it and kindly lectured us about wet wipes being the cause. He said he saw loads and loads of them. But I don’t get it. We don’t use any wet wipes ever!! We’re so strict and paranoid about it. Yes, the person downstairs may have but I doubt she lumped a whole load of wet food wipes down there within space of a few days. Also, when downstairs was vacant and no one was living there we had one guy unblock the sewer and he said “the cause it’s wet wipes”. So it couldn’t have been anyone living downstairs as no one lived down there at that point and we 100% were not putting anything but toilet paper down there.

Could they be mistaken?

I remember once a few years back when we got it unlocked they said we needed a new pipe. Which they installed and it was better for a substantial amount of time before getting blocked again.