Ahhh help with 4 year old please!

[NoNameIdeas]

Need help with my 4?year old ds, I've run out of ideas!
He is (and has been for ages) toilet/potty trained, happy to go by himself at home and nursery and with help when out somewhere new...but only for a wee! He refuses to poo anywhere other than in his pull up (still has at night as not fully dry at night yet).
He recognises when he needs to go and will ask for a pull up of it is the daytime, do the poo and then happily go back to his pants. This was fine to start with but he will be going to school in September so obviously not ok for much longer! If we are out or we say no to a pull up he will just wait until he has his bedtime one on and then go, or just not go at all.
We've tried sticker/reward charts, making pull ups just for night time (but then he waits!), different types of potty/toilets, reading books/iPad time whilst he tries to go but still no joy! We even tried saying he could have a toy he really wanted if he did it, but he just said that he didn't want a toy!

Does anyone have any advice or tips I can try?
Thank you!

Is he able to tell you why he won't poo in the toilet? Do you get him to change his own nappies? I'd start with that.

@NoNameIdeas
What ohalrightthen says..plus it sounds like your bribes don't have enough value to him.
Everyone says don't use food as a reward, but I got desperate and told my son that could get one chocolate M&M candy if he pooed in the toilet and one extra if he washed his hands afterwards. We very rarely allowed him to have candy any other time so it had a gigantic reward value to him. He was trained in about 2 days and I slowly stopped the candy over a course of 5 days...he realised how much better it felt to poo on the toilet instead of a pull-up so that became his reward.
Please don't chime in as to what a rotten mum I was ...I was desperate and it worked...it was getting ridiculous to try to clean up a pooey pull up on a big ole child... It was a mess even at the best of poos
And he was very proud of himself!

Can you kind of open out the pull up and lay it in the potty so they "go" in the pull up on the potty as kind of a mid way step. Then eventually reward his way to taking away the pull up? I think I read this tip on here, then told my sister in law who used it wirh her son and worked well.

Also the Eric website

I could have written this post myself OP! My DD is 4 and also will not poo in anything other than a pull up. I've also tried everything. I'm at a loss!

Thanks so much for all your suggestions, love the idea of putting the pull up inside! Will look at Eric tonight.

@MonicaGellerBing I'm glad it isn't just us! It's so tough!