What are the most absorbent adult diapers? He is soaking through 3 depends!

My grandmother cares for my cousin (her grandson) full time. He lives with her and suffers from Leighs Disease. He has had alot of kidney and bladder infections lately and I think he has gotten used to holding it in now because it burns so we have had to put him in diapers because once he tells us he has to go we can't gt him there in time because he has waited so long. He is 20 and only crawls so we have to use a urinal jug instead of trying to stand him up. We are currently having to put 3 depends on him at a time and he is still soaking his clothes through that. He's full care and it's so hard on my grandma to have him change his clothes all day long. Are there any other diapers we could order that would be more absorbent?