Under the IPC & IRC the maximum length of a fixture arm can be computed by dividing the diameter of the drain by the pitch. If an 1-1/2" line is installed with the code standard 1/4" per foot pitch the maximum lenght would be 1.5 / .25 = 6ft but in this instance the line has a 1/2" pitch so the maximum allowable length would be 1.5 / .5 = 3'. (The bottom of the drain line at the trap weir may not be higher than the top of the line at the vent opening). Both the configurations illustrated above would not pass code for a number of reasons. The simple solution would be to remove the drum trap & extend the length of the tub drain tailpiece. Code will allow up to 24" vertical drop from the tub drain opening to the water level in the trap. Attach a P-trap and run the line with a 1/4" per foot pitch. A wye can be installed on the drain line with the side input angling downstream. You can then put a street 1/8bend on the wye side opening input, which would turn the side opening vertical and attach an AAV where the base of the AAV is 4" above the drain line. REF-IPC 917.4 Location. The air admittance valve shall be located a minimum of 4 inches (102 mm) above the horizontal branch drain or fixture drain being vented The air admittance valve shall be located within the maximum developed length permitted for the vent. The air admittance valve shall be installed a minimum of 6 inches (152 mm) above insulation materials.

I think the prices your friend has asked for are reasonable - even a good buy for the sink. I bought a floor model after the sink was discontinued for $580. At the time (almost a year ago) the best online price I could find was $676. Those deep sinks are expensive! I paid $38.50 for my sink grid on eBay but typical online price was $95. I haven't checked lately, but I think that grid is still available. My dishwasher is to the right of the sink, perpendicular to the sink counter, closest to the small sink with the disposer. My faucet is Blanco Anu. I love the high arc but find the pullout style awkward. Once pulled out, it is hard to aim the water spray where it is needed. I would suggest looking for a pulldown style, instead. (There's an active thread about pullout versus pulldown faucets that you may want to view, too.) I don't notice much splashing from the small sink. Rather, the tall faucet seems to splash more in the large sink and on the divide between the sinks. I don't find that a major problem - just a quick wipe with the sponge and all is neat again. The stainless does seem to show water spots easily. I've tried a couple of stainless cleaners and the Weimar polish seems to do the best job of preventing water spots. You do need to wipe off the water, though, when you are through using the sink. And our water is very hard.

I had a hard time deciding too. I took a hard look at how I use my sink (currently a double). We have a garden and belong to a CSA, so I soak a lot of veges on the right side while cleanup is on the left. I also like to wash on the left and drain the clean items on the right. I wanted to be able to lay cookie sheets and long pans flat too. I found a sink that satisfied both needs. I'm getting the Franke PRX120. I love this particular sink because it only needs a 39" base cabinet, whereas similarly sized sinks require a 42" base cabinet. Plus it has an integral shelf (optional) that you can rest a grid on that raises up the bottom so you don't have to reach in as far when you don't need to. I can lay flat my biggest cookie sheets and baking pans. It is stainless steel. In the end though go with what you like best, most people have definite preferences one way or the other. Do you know someone with a single bowl that you can try out the way that you'd be using it?

Do you have a disposal? If so which side would you utilize it in? I had a SS sink that was set up like this and I hated it. The large side was fine but the small was useless. It splashed water everywhere and the disposal was on that side. So dumping large pans of water - spaghetti, corn on the cob or what have you it could not handle it. It does appear that the smaller side is the same depth as the larger which will help with splash (mine was more shallow - even more absurd). It really just wasn't a versatile or useful basin at that size. I have the blanco precis low divide (due to 33" sink base). I like it well enough but had my sink base been 36" I'd have gone with the 36" super single without batting an eye. You might want to check that one. It's made for draining and I think it's laid out more usefully than the 1 1/2. It's a low divide so you can still fit most things in it flat but if they are really large the angle is not as harsh. I do stand things up to dry in it on occasion and it works perfectly for that. I would look at what you hope to do with that side and then what you normally do most of the time and then go from there. I love my blanco sink - it is so easy to care for - no scratching, it's quiet. Love it. edit: Oh I want to add - if you can go look at one in person. That will probably tell you all you need to know. It's so hard looking on line. edit #2: (lol) My only sink is also in the island.