seems like the basic yes/no answer will have to come from my inspector.
hj, could you please elaborate? did you mean 'vent pipe' rather than 'drain pipe'? or were you just commenting on how i probably don't get very good drainage now with my 1.5" drain line? the reduction you're referring to is going from 2" drain to 1.5" vent? the following paragraph hopefully gives a better picture. i understand that my 2" drain won't drain optimally with a 1.5" vent but it should be an improvement over 1.5" drain line, and if the inspector will be happy then i'll be happy.
after the trap, the drain goes horizontal (with slope) about 1' to a Tee that has a vertical vent pipe that goes straight up through the attic and out the roof (about 20'). the drain line then goes horizontal another 2', then down 10', then horizontal (with slope) another 8' before it feeds into the main stack about 6' above the basement slab.
my idea was to replace the drain line all the way back to the stack with 2", and re-attach to the existing 1.5" vent pipe by means of a reducing bushing just above a new Tee. i have plenty of vertical wiggle room in the joist cavity for the bigger pipe/fittings/bushing.
oh and currently it's all galvanized back to the cast iron stack.
is there any reason not to have at least a section of galvanized? that last horizontal run to the stack is only about 6' above the basement floor and i'm worried that plastic might succumb to, say, a 4-year-old whacking it with a broomstick. the basement is our playroom.
thanks