Yep, it's literally sold as drain cleaner. Just be sure it's compatible with your sewage disposal system (e.g., some septic tanks might not like it). And also, if it seems like a lot of the naphtha has remained trapped in the sludge it would perhaps be environmentally more responsible to let it air in a wide pan before pouring. Mind you, the amount is most probably peanuts compared to runoff associated with motor traffic - so you can weigh that up against the safety considerations of having a pan of caustic sludge sitting around in the open. If both of these factors bother you then by all means just add a suitable dash of vinegar before leaving the whole thing to evaporate, at which point you could dump it in the compost or use it as mulch.