If you want the ballvalve outside the box you could even stick a pushfit straight to the tank and run the nylon to a ballvalve outside the box if you wanted.
thks, that’s what i was thinking , but now drill a hole through the side of the box, then the valve can be clipped to the outside of the box with the drainage hose in it so it’s neat and tidy
many thks and easy when u know how,