Hi Levantine,
I have some experience of this as my ten year old ds has always been in pull ups until very recently, and 9'times out of 10, absolutely soaks them, often through to pjs and even sheets.
At age 7 he was seen by the school nurse and she tried to increase his bladder capacity by getting him to drink lots in the day. We kept lots of charts - had to write down how much he drank, measure his output one a day etc. Unfortunately he still soaked his pull ups at night. For a while after that, I decided that we should just let him outgrow this in his own time, but that didn't happen.
Earlier this year, we changed his pull ups to an enuresis alarm (the rodger one) which makes a loud noise as soon as ds starts to wee. Theory is you then get up, ds goes to the toilet, then changes his pants, reattached the alarm, then goes back to bed.
That was met with quite a lot of success, and really saved on the washing, though we often found ourselves trying to wake a very drowsy boy to go to the toilet! We had a dual alarm, ie when the alarm went off in ds's bedroom, it also went off in ours.
Just a week ago, after being referred by our doctor, we saw an enuresis consultant who prescribed our son with a tablet which he puts under his tongue each night before bed. And so far we have had 5 out of 5 dry nights! The tablet tricks the body into doing what it should do naturally, which I to stop the production of urine at night. The tablet is called desmopressin. We have to go back for a review in 3 months.
I must admit, I don't particularly like him taking medication, but I think the dryness is good for his self esteem, and certainly makes my washing load less.
Hope that helps.