studor vent(AAV) are not allowed in many areas. it all depends on your local codes. the easiest way to find out is to call teh local permit office and speak to the inspector. then GET IT IN WRITING when you pick up the permit that the AAV is allowed. you would be surprised how many folks are told by "someone" at the permit office that soemthing is ok, then when the inspector comes it is not allowed. the best bet is to take a set of drawings along when you go to get the permit and have them stamp it approved, then you have a leg to stand on if the inspector does not like it.

The simple answer is "NO". A vent line may not be run horizontal until it reaches an elevation of 6" higher than the highest fixture served by that vent. If you are under the Uniform Plumbing Code you would be required to run the vent through the roof as your plumber has suggested. If you are under the International Residential Code you could install an AAV(air admittance valve) on a riser at the washing machine location.

It comes down to how powerful the washing machine pump is... Now, this check valve has to have a reasonable bore, what's a washing machine outlet - 3/4" at least? The big risk here - ok there's two - one is, as Pinoke says, you might end up with sewer gas being sucked into the place, which, in a well-sealed house (as most are) could be lethal, maybe even explosive. The other risk, more likely, is a failure or blockage of the check valve which could result in raw sewage being siphoned back into your basement. If you chose this route, I wonder if your insurance would pay out if something went wrong. Don't get me wrong, provided the lift's not too great (and you'd definitely need a trap etc some distance ABOVE the sewer line to reduce the risks, this ought to work, however, and I'm not sure about whether all ejector pit things have to be buried - I've seen one of these ejector units and they don't look that complicated or expensive, and the BIG advantage is, you can have a laundry sink down there too, which will drain into one of these gizmos - and will pump itself out up into the sewer when it fills - and these things are designed for the job and ought to do it more efficiently and safely - and when you sell the house, you won't have to rectify anything, as if you take the cheap route, you might be forced to disclose it, or an adept building inspector may spot it and put you in an unfavourable bargaining position.

The pan has a threaded connector to allow the pan to drain into the floor drain. The threaded connecter sits proud of the bottom of the pan by approx 1/8" so if I just pour water into the pan now and then, most will drain out but not all since the threaded drain creates a small lip (see attached photo for example. It also creates a potential opportunity for a leak which is why I'm not crazy about the idea of just pouring water in the pan. Instead I may snake a small 1/4" or 3/8" tube into the drain and have that run under the washing machine and up the back so I can fill it from up top and keep the pan pretty much dry. Anyway, I'm surprised I'm having to go through such a DIY solution as it seems like this would be a relatively frequent problem for this type of floor drain/pan setup.