I am going on a serviced pitch for a change, how much waste pipe would be advisable to buy?

Difficult to say as I understand serviced pitches can vary. This may help. https://caravanchronicles.com/2013/05/26...rviced-pitches/

Collapz waste pipes are great and a bag of four meets most needs.

Thanks, I have gone for 7 metres of pipe and put it in a EHU bag, my drain is opposite my door which means if it is nose out the pipe has probably got to go around the back of the van to get to the drain

What is the best way to clean the waste pipe after use ?

With the Collapz pipe set you get a long handled brush with a loongth of chain attached so you can pull it through.