I use brass because it's really available, strong, corrosion resistant and cheap.
If you have access to stainless fittings (most of us do not), think about how much better that would be than a piece of ABS.
Most stainless I have used has been unreasonably heavy, not to mention expensive.
GT
Speaking of heavy, how do you secure the 3/4 mpt fitting, 3/4" ball valve, 3/4" mpt, 3/4" hose bibb adapter, garden hose female, hose barb combo? Just clamp it to the stringer?
Mine's setup so the the engine flush part is removable when I'm not using it. However, everything else just rests on the floor of the bilge and I'm not a fan of that.