Need help with males anal gland issue

My fiance and I have 4 cats in total, 3 girls, 1 boy. The girls have no issues at all, but the boy cat doesn't clean his bum. He has poop on it all the time and we keep having to wash the sheets, blankets and pillows on chairs because he gets poop or some anal juice on them.We've been to the vet and she said he was fine, he's just a slow learner. I've tried getting the other cats to clean him (they usually do), Ive sprayed his bum with a little bit of water to see if he would start cleaning himself (he just sits down and doesn't clean) but nothing seems to be working. 

I'm 7 months pregnant and I don't want him to get poop or anal juice all over the babys stuff, so we might have to get rid of him if we can't figure something out. Does anyone have any ideas on how to get him to clean his bum ? 

I'm not sure if this will work for your cat or not, but I remember when we were kids and one of our cats didn't clean herself very well my Mum put butter on her butt to encourage her to clean it.

It won't do him any harm and he might get the idea.

Maybe leave him somewhere he can't get butter over the furniture for an hour or so to see if it works though.......

Thanks! I'll have to try that, I was also told to try cat nip spray. 

What kind of food are you feeding him--what is the consistency of his poop?
I ask because generally if the feces are hard enough (but, alas, not too hard/too soft), then the anal glands are expressed naturally via the pooping mechanism.
It can be a delicate balance and frankly I'm not sure how to balance it (I fed prey model raw). Too much fat; too little fat; too much dry food; a slight allergy to the food can all disrupt the consistency of the poop to varying degrees.
Try altering his food a little if that is possible/practical.