Originally Posted by dznf0g
The black tank is the one, usually, directly below the toilet...and usually the one closer to the rear axle. But not always. Depends on Floorplan.
Though this is typically the case, the 33' Classic and the 30' Bunk- (at least starting, the last few years), these two units have macerator toilets where the black tank is not directly under the toilet. My understanding is that this was done because the head is in the back and the back has somewhat limited tank capacity that far aft. For example, early 30' bunk models had a roughly 18 gallon black tank capacity with the bomb drop gravity type toilets. This similar layout was and may still be found in the 19' unit, that back in the early 2000s had a 9 gallon tank before it was increased to around 18 gallons. Given that the 30' bunks can sleep upward of 8 (approx), I think AS went to a macerator toilet so they could get more tank capacity by pumping it to a larger black tank closer to the axle.
The logic here seemed flawless- except that they also needed to increase the water tank size since those macerator toilets use a lot more water than the old gravity bomb toilets. In my mind it's a net zero gain, but it sounded like a nice idea. In practice I personally know the black tank fills faster as does the fresh water tank drain faster too compared to the gravity bomb droppers, but I digress......
To answer the question, if your 33' unit bears any resemblance to my 30' bunk with the macerator toilet, the black tank may be the tank just aft of the axles. Keep in mind that the OPs trailer is a 33' from 2018 and mine is a 2021 30' bunk. Not sure if 2018 started the macerator in the 33, but my guess is yes, given the premium amenities and place on the Airstream model food chain. I would guess the 33' had it first and then it trickled down as many things do from the Classic line.