Getting teenage son to do what counsellor says and help himself

Having a hard time with this. 

We've had issues with taking his medications. Didn't take for about a month because he "forgot". Now we have to supervise him at same time every day otherwise he wouldn't take them. We were out the other night and gran was at home looking after - he forgot. One day on his own. 

Very annoying because these meds do help him a lot. And to get this we've had to pay over £400 in private psych fees and take him to appointments an hours drive away!

Hes seeing CAMHS at the moment and the counsellor is pretty good. She comes up with things for him to do. (His OCD/compulsions) are to do with bathroom rituals. Previous appt he had to try and cut one thing out.

Did he bother to try? Nope. Not at all.

Last time, she gave him sheets to fill out to time himself. She suggested we get a timer so we did. Week gone by now has he done it - nope.

We tried the positive approach - we'll give you x if you do it for x days - Nope.

We've reminded him nicely 2-3 times. We've upped it and said he needs to follow advice - nope. We gave him a final warning. Last night we had the "I forgot" excuse again so he lost the use of his PC which he was not happy about. We had no other choice.

Part of the problem is his PC. All he cares about is getting back on his PC asap. Which is why other things take a back seat. We've got 2 bathrooms and another toliet at home. If he spends an hour in there (which he does) then it doesn't cause much hassle. We tell him not to use all the hot water but he ignores us (it has no effect on him he doesnt pay the bills!)

We're going away shortly - there won't be three toilets. It will be a problem but I know full well he won;t give a monkeys. He rarely wants to leave the house because of things like this. We've managed to stop it now but we;'ve had some nightmares with public toilets with him. He used to like to spray EVERY surface (it would be like it had rained in the bathroom) and spead toilet roll on every inch of the floor. He once completely blocked (and they had to close it for the rest of the flight) toliet on a plane which was not cool.

Hes happy to go to appointments but makes no effort to try to help himself. He just wants to carry on as normal and not make any efforts. Its all too easy for him at home but of course life isnt like that. He seems to be blinkered to just seeing PC games, go in toilet/shower at home for an hour if he likes and nothing else.

Hes ok in school - but he just doesnt use the toilet - which is not reallty a solution but hes happy to just go with it. (although in the past we have caught him taking anti diarhoea tables out of the cupboard to stop himsef needing loo at school - that wont end well with everyday use of course).

"You can lead a horse to water" etc. We just don't know what to do to encourage him....