Thanks speedball for the information, the lavitory drain is already vented if I tie into it do I need to run a new vent pipe through the roof?

50myass... I believe I posted to your question... not speedball. At least I was the one that posted to your question about washing machine into lavatory earlier today. Would be great for you to repost this question over to the original post so others can follow step by step as we go through things. ANyway, let me know.

Sorry massplumber2008, and thank you for the information so if the lavatory drain line is vented, if I tie into it do I need to run a new vent pipe through the roof?

NDB... yes,you would need to vent the fixture... but may be able to connect it back into the lavatory vent (as you suggested) as long as connect into the lav. Vent at least six inches higher than the flood level rim of the washer AND the lavatory. That is allowed and may save you the hassle/time of penetrating the roof.