Not that I'm aware of but I don't know crap about boilers. There is one main drain in the middle of the floor so my guess is if there was a drain it would feed into the central drain in the floor. Looking around it I don't see a secondary drain and everything down there is dry.
I've ordered some green water leak tracer, I'm going to re-test the toilets as soon as I get it to be 100% sure. It is a very slow leak, like just a small trickle into the septic.