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This could refer to either tank drain valves or low-point drains for the water supply system.
If they’re waste tank drain valves, then you might have tanks fore and aft of the axle to help even out the loaded weight. This is quite common on larger rigs, especially if you have three waste tanks.
If they’re low-point drains for the PEX pipes … then it’s possible the manufacturer just didn’t plan out the water supply runs very carefully and just put a drain wherever it was most convenient, or wherever the water lines dipped to their lowest point.
But it’s also possible that the designer wanted split drains for serviceability. Or maybe testing showed that the system drained faster or more completely with a different location.
No matter the reason, I’m sure it’s annoying to have to walk around the camper to access all drain petcocks for winterization!