Any advice for DS' "leaking" accidents

[logan's mom]

DS1 is 3 years and 1 month old. He has consistently pooped on the potty since 14 months....no problems there! He has used peed in the potty for over a year. He does great at school and when we are out but at home he holds it until he is literally leaking pee. I am tired of washing underwear all day!!! I ask and ask if he needs to potty but he says "no" then a few minutes later will run to the potty like his pants are on fire because he is dying to go.
Making him try equals tantrum.

He has been dry through naps and overnight for months...

I just don't get it.

Any advice?