Can I mount my air tank on its side?

Sorry if this isn't the right place for this.

I've just got the stanceparts air cups and just want to check if anyone's had any issues mounting an air tank on it's side? I've seen some people do it but just want to make sure its fine before I do, as the manual says not to but doesn't give a reason. I can only assume condensation but not sure how much of an issue that actually is.